SMITHSONIAN MISCELLANEOUS COLLECTIONSVOLUME 87, NUMBER 14
THE FUNCTIONS OF RADIATION IN THEPHYSIOLOGY OF PLANTS
II. SOME EFFECTS OF NEAR INFRA-RED RADIATIONON PLANTS(With Four Plates) ^.,-rr^HUW I .^is]777/'7?>s.y^^ NOV 15 1932BYEARL S. JOHNSTON "Division of Radiation and Organisms, Sniitlisonian Institution
(Publication 3180)
CITY OF WASHINGTONPUBLISHED BY THE SMITHSONIAN INSTITUTIONNOVEMBER 15, 1932

SMITHSONIAN MISCELLANEOUS COLLECTIONSVOLUME 87, NUMBER 14
THE FUNCTIONS OF RADIATION IN THEPHYSIOLOGY OF PLANTS
II. SOME EFFECTS OF NEAR INFRA-RED RADIATIONON PLANTS(With Four Plates)
BYEARL S. JOHNSTONDivision of Radiation and Organisms, Smithsonian Institution
(Publication 3180)
CITY OF WASHINGTONPUBLISHED BY THE SMITHSONIAN INSTITUTIONNOVEMBER 15, 1932
Zf)c jSorJ) (gaitimovc (prceeBALTIMORE, MD., U. S. A.
I
THE FUNCTIONS OF RADIATION IN THE PHYSIOLOGYOF PLANTS
II. SOME EFFECTS OF NEAR INFRA-RED RADIATION ON PLANTSBy earl S. JOHNSTONDivision of Radiation and Organisms, Smithsonian Institution(With Four Plates)Experimental results bearing on the influence of near infra-redradiation on plant growth and coloration are presented and discussedin this paper. Plants were grown under two different radiation dis-tributions of equal visual intensity, one limited entirely to visibleradiation, the other including a large amount of energy in the nearinfra-red. These preliminary experiments are a part of the programbeing undertaken by the Smithsonian Institution bearing upon thefunctions of radiation in various plant processes. A description ofthe special equipment (see pi. i) that has been developed for thestudy of the effects of radiation upon plants grown under controlledconditions has been given in another publication (5).^CULTURAL METHODSThe tomato plant was selected for these experiments because con-siderable work (12, 13, 14) had already been done with it in waterculture and many of its growth characteristics are known. Further-more, it has been used as an indicator plant (10) for determining thedeficiency of certain fertilizer elements in the soil, and it respondsvery quickly to unfavorable atmospheric conditions. Because of itsquick response to slight environmental changes its behavior is anexcellent criterion of those conditions.Tomato seeds of the Marglobe variety were germinated betweenlayers of moist filter paper in a covered glass dish at a temperatureof 25° C. When the roots had grown to a length of 2 to 10 mmthe young plants were transferred to a germination net. This netwas made by stretching two pieces of paraffined cotton fly-nettingover a circular glass dish 19 cm in diameter by 10 cm deep. The
^ Numbers in parentheses refer to the list of Hterature cited, found at the endof this paper.Smithsonian Miscellaneous Collections, Vol. 87, No. 14
2 SMITHSONIAX MISCELLANEOUS COLLECTIONS VOL. 87two pieces of netting were separated by a piece of glass rod 0.5 cmthick, bent to fit inside the dish. As the roots grew through themesh the two layers served to hold the plants in an upright position.Flowing tap water was passed through the dish in a manner tokeep the upper layer of netting afloat. The plants were illuminatedby a 200-watt Mazda lamp placed 30 cm above the netting. Laterallight was cut off by surrounding the germination net and plants withblack cardboard tacked to a light wooden frame. This frame wasraised above the table level and was large enough to provide ampleair circulation around the plants. When the seedlings were approxi-mately 3 cm in length they were transferred to the culture solutions.Each culture consisted of a single plant supported by means of cottonin a small hole in a paraffined flat cork stopper which fitted into a2-quart Mason jar containing the nutrient solution. Four of thesejars were then screwed to the under side of the bottom plate of eachgrowth chamber ; the young plants extended through the holes intothe chamber.The nutrient solution was made up of the following salts withthe corresponding partial volume-molecular concentrations
:
Ca (N03)2 0.005Mg SO4 0.002K H2PO4 0.002Mil SO4 0.0000178H3BO3 0.00005The approximate calculated concentrations of the nutrient ions in thissolution expressed as parts per million and milliequivalents are
:
Ppm. Millicciuivalents "Ca 200 10.Mg 49 4-0K 78 2.0NO3 620 10.SO4 194 4.0POi 190 6.0Mn I 0.0364B 0.55 0.15
° Calculations based on milliequivalent per liter ;= — x ppm.at. wt.To this nutrient solution was added humic acid ^ containing 2.4 mgiron per cc at the rate of 0.5 cc per liter of nutrient solution. The
^ The humic acid used in these experiments was supplied by Dr. Dean Burkof the Fixed Nitrogen Research Laboratory, United States Department ofAgriculture.
NO. 14 EFFECTS OF INFRA-RED OX PLANTS—JOHNSTON 3method of making this iron compound has been described and dis-cussed by Burk, Lineweaver, and Horner (6). This compoundpromises to be a very useful source of iron for nutrient sokition ex-periments. UnHke most of the other iron compounds used in thistype of work, the sokition contains very httle if any precipitate,even at high pH vakies. Hence it is not necessary to add this formof iron every day or two during the early stages of growth as mustbe done with ferric tartrate and some other iron compounds. Oneapplication of iron humate is sufficient to keep the plants greenunder good growing conditions for at least two weeks.EXPERIMENTAL PROCEDUREIn the experiments herein described, only the overhead illuminationwas used. The light period for each 24 hours extended from 9 a. m.to 12 midnight. This period of illumination (15 hours) falls withinthe optimum range for tomato plants. Two wave-length ranges fortwo different light intensities were used. One wave-length range in-cluded all radiation transmitted by a water cell 1.5 cm thick withpyrex cover glasses, and the other was further limited by a heat-absorbing filter. Two chambers of each pair had the same visualintensity. It is realized, of course, that the radiant energy requiredin plant reactions is not exactly limited to the visible region, noris it at all likely that their requirements are at all proportional to thevisibility. It would be preferable to compare the effect of radiationin the range absorbed by chlorophyll with radiation including thenear infra-red as well. Practical considerations make it necessary touse a heat-absorbing fdter which cuts off not sharply at the limit ofchlorophyll absorption, but gradually from 6,000 to 8,000 A. Themethod to be described for equalizing the visual intensities is simplya convenient means of attaining approximate equality of intensitiesin the visible range common to both types of radiation.The light intensities were equalized at the beginning of the ex-periment by means of a Weston photronic cell provided with a specialheat-absorbing filter (Corning heat-resisting, heat-absorbing, darkshade filter 2.82 mm thick). At the conclusion of the experiment oftwo weeks' duration the light intensities gave the values indicatedin Table i. This combination yielded a sensitivity curve shown as acontinuous line in Figure i. Sensitivity is plotted as ordinates in arbi-trary units with 100 as maximum against wave lengths in Angstromunits. The visibility curve shown as the dash line is included in thisfigure for the sake of comparison.
4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8/The two distributions of energy, adjusted for equality for visibleradiation measured as indicated, are shown in Figure 2. In order todetermine the distribution of energy in the chambers with and with-out the heat-absorbing filters, a curve of relative emission per unitwave length of radiation for a tungsten filament at the absolute tem-perature of 2,980° K. was constructed. This tungsten radiation curvewas then corrected for energy absorbed by the pyrex filters and1.5 cm of water. Another curve was obtained by further correctingfor energy absorbed by the heat-resisting, heat-absorbing light shadefilter (8 mm thick) and 1.5 cm of water. From each of these twodistribution curves corresponding response curves were drawn byTable iLight sources and iutcnsittcs
Chamber
NO. 14 EFFECTS OF INFRA-RED ON PLANTS—JOHNSTON
3000 4000 5000 6000 7000 8000Fig. I.—Sensitivity curve (continuous line) of a photronic cell provided witlia special filter, and the visibility curve (dash line).
Fig. 2.—-Curves showing the two types of energy distribution adjusted forequality of " visible " radiation as measured by the photronic cell with its specialfilter.
6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8/
freely exposed to the air. Temperatures were usually read threetimes each day. During the light periods the temperatures wereapproximately 3.5° C. higher than during the dark periods. Theaverage temperatures are shown in Table 2.In this experiment no measurement was made of the rate atwhich air was recirculated through the chambers. Fresh air wasinjected into the system at the rate of 15 liters per minute. Itshould be emphasized that a sufficient rate of air movement in plantgrowth chambers is very essential. It is true, as has been discussedby Wallace (20), that some plants have been grown for severalmonths in glass containers hermetically sealed. Few plants, how-ever, are suited to such an existence and then only when there is aproper balance of mineral and gaseous elements, temperature, andlight in their microcosm. In two previous experiments air was
Table 2Average air temperatures in the plant groiuth chambers
Growth chamber
NO. 14 EFFECTS OF INFRA-RED ON PLANTS—JOHNSTON 7
of four plants each were grown under uncontrolled conditions innatural light, one group placed in a west window of a room in theSmithsonian tower, the other standing in the north window of thebasement laboratory. At the end of two weeks the plants were photo-Table 3Plant data at harvest, expressed as averages per plantRadiationIntensity Low
Distribution" V and I
Plant group.Dry weight (mg)Tops 126Roots i MTotal j 140Water absorbed (cc) 45Stem height (cm)FinalIncrease 20.217.2Number of leaves.
.
Order of greenness.Water requirement 320
„ root ^Ratio wt.top
16319
6.84-44-3
I
High DaylightVandl
810
4264046688
t8.o15-6
-..8
Westwindow
RatioInternodal indexstem ht.no. of leaves
RatioStem elongation(final ht.original ht.)
4.0
6.7
1.6
2.8
igg3123093
12.79.95.83
16230192
Northwindow
40:
7.85-45-44
1631918
5.63-53-52
0.09
3-1
7-5 4.5
444
0. 18
1.3
3.^
956
o.i;
1-4
" V and I, visible and near infra-red radiation; V visible radiation.graphed and measured. The plant data obtained from these measure-ments are presented in Table 3.In an examination of the data of this table it should be rememberedthat the visible intensities in chambers i and 2 were approximatelythe same. Likewise those of 3 and 4 were alike. However, in thelatter pair the light was much more intense. In chambers 2 and 3
8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8/
the infra-red was removed. A comparison of the dry weights showsthe greatest growth to have occurred in chamber 4 and the least inchamber 2. In a subsecjuent experiment, similar to this one exceptthat the temperatures were higher, the same order of growth, asmeasured by dry weight, existed between the four chambers. Thatis, in order of plant dry weight the series in this and a subsequentexperiment was 4, 3, i, 2 (high visible plus infra-red, high visibleonly, low visible plus infra-red. low visible only). It is also ratherinteresting to note that the growth of plants in chamber 2 (lowvisible) was very similar to that in the north window of the laboratory.Also there was a good deal of similarity between the plants in cham-ber 3 (high visible) and those grown in the west window of the tower.A greater amount of water was absorbed by the plants exposed tothe greater light intensities—those in chambers 3 and 4. It shouldalso be noted that in chambers i and 4, where the proportion of redand infra-red was greater, the plants elongated much faster thanthose in chambers 2 and 3. Although there was little difference foundin the average number of leaves of plants in the four chambers,there is an indication that more leaves were produced in the moreintense light.Attention is directed to the order of greenness of the plants grownunder these six conditions of illumination. Those grown in chambers2 and 3, which received only visible radiation, and in the north windowwere greener than the others. The lower leaves of the plants inchamber 4, where the radiation was more intense and included infra-red, had turned yellow. Those in chamber i, while not as yellow asthose in 4, were far from a healthy green color.In the lower part of the table several derived values are tabulated.Water requirement is here considered as the amount of water ab-sorbed by the plant during the two wrecks of growth per unit oftotal dry matter. Plants in chambers i and 4, where infra-red radia-tion was present, were more economical in their use of water thanthe others. The ratios of root to top dry weights indicate that some-what heavier roots in proportion to tops occur without infra-red.The internodal index was determined by dividing the height of theplant by the number of its leaves. It gives a relative index of thelength of internodes. This index as well as the ratio of final tooriginal height of the plants shows that much less elongation occurswithout infra-red.Plate 3 shows the general appearance of the six groups of plantsafter two weeks of growth under the conditions of light mentioned
NO. 14 EFFECTS OF INFRA-RED ON PLANTS—JOHNSTON
in this paper. With the exception of set i all the individuals of thevarious groups are very uniform, with but slight variations. Forbetter comparison a representative culture from each group wasselected and photographed. These are presented in Plate 4-DISCUSSIONGrowth of plants under different wave lengths of light has re-ceived considerable attention at the hands of plant investigators.Much of this earlier work has been reviewed by Teodoresco (18, 19),who has done very valuable work along this line. He investigatedtwo main spectral regions (the blue-violet and the red-orange) bymeans of colored solutions and glass filters. Because of the generalconclusion of many previous investigators and his own experiencethat infra-red has no appreciable effect in addition to heatmg. hedid not think it necessary to use water screens between his lightsources and the plants. However, in measuring his light intensitiesa screen of water and copper acetate was used to eliminate the effectof the infra-red upon his measurements. His general conclusionsfrom experiments with a large number of land plants, many of whichwere duplicated with both glass and solution filters, are: that inthe longer wave lengths, internodes were elongated and more numer-ous areas of leaves reduced, the leaves themselves were thinner,and a general abnormal configuration resulted. In the shorter wavelengths growth in length was retarded, leaf area increased as well asleaf thickness. The general appearance of the plants was normal,resembling those grown in white light. In many respects the plantsgrown in the red-orange region resembled plants grown in darknessexcept for their green color. As Teodoresco points out, plants grownin darkness became etiolated without chlorophyll assimilation, so thatgrowth ceases. In red light, however, the plants grow for a longer timethan in darkness, due to the production of food by photosynthesis.In view of the fact that different color filters usually transmit dif-ferent amounts of infra-red light, the existence of an effect of radia-tion in the near infra-red would necessarily qualify the conclusionsto be drawn from such experiments. Consequently, the results otthe present investigation raise serious doubts as to the validity ofthis type of experiment, unless it is definitely shown that the differentfilters transmit the near infra-red in the same degree.Funke (7), working mainly with aquatic plants, studied the effectsof three general spectral regions, red, green, blue, and subdued whitelight Any ultra-violet or infra-red passing through his filters was
10 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 87
neglected. The intensities behind these filters were approximately25 per cent of the energy of diffused daylight. For many speciesthe light intensity was insufficient. Results were obtained for plantsin which photosynthesis was greater than respiration. The anatomyand behavior of plants in the blue light resembled those in fulldaylight. Those in red were " etiolated as in darkness (except ofcourse that chlorophyll is formed). In green, phenomena are eitherthe same as those in red or development is reduced to a minimum ;the latter is undoubtedly due to a total absence of assimilation ofcarbonic acid. In gray, development now resembles that in blue, nowthat in red, depending on the needed quantity of blue rays beingsmall or great."Arthur, Guthrie, and Newell (3) have carried out a great manyexperiments on the growth of plants under artificial conditions andfind the tomato the most sensitive to high light intensity in com-bination with a long day period of illumination. In three series theyused respectively 5, 7, 12, 17, 19, and 24 hours of illumination daily,with an intensity of 450, 800, and 1,200 foot-candles. The air tem-perature of the first and second series was maintained at 78° F.and the third at 68° F. Their results show that the tomato will notwithstand a 24-hour day of illumination at intensities which causelittle or no injury to other plants. Even 19- and 17-hour days areinjurious at the higher intensities. In the greenhouse experiments,where the plants were exposed to 12 hours daylight and 12 hoursartificial light, the plants were injured. However, the rate of de-velopment of this injury was decreased by this combination of day-light and artificial light. The injury was characterized by the leavesbecoming faintly mottled with necrotic areas appearing along theveins. The plants also had yellow leaves. The first signs of injuryappeared in five to seven days.In commenting on the illumination used these authors state
:
The energy value in the constant-light room calculated at 0.3 gram caloryper square centimeter per minute amounts to approximately 12,960 gram caloriesper month of 30 days. The total for the month of solar and sky radiation aspublished by the New York Observatory for June, 1929, was approximately11.903 gram calories. The two energy values are similar but, as already pointedout, the spectral distribution is in no way comparable. The glass-water filterin the constant-light room absorbs practically all radiation of wave-length longerthan 1,400 niM so that the total energy value of 12,960 gram calories includesonly the visible region and the near infra-red of wave-length shorter than1,400 m/x.
NO. 14 EFFECTS OF INFRA-RED ON PLANTS—JOHNSTON IIThe experiments described in the present paper set forth the gen-eral growth characteristics of tomato plants grown under two rangesof wave lengths for two different intensities. One group of plantswas exposed to light, a large proportion of whose energy was in thered and near infra-red region, the other exposed to light limitedto the visible wave length region. Thus, an attempt is here made toseparate any near infra-red effects from those brought about byother wave lengths.The growth of these tomato plants as measured by their total dryweights clearly shows that the plants receiving infra-red radiationwere considerably heavier, with less difference occurring in thestronger light. It is conceivable that if the illumination were furtherincreased the plants receiving no infra-red would surpass in weightthose receiving these longer wave lengths. Such an increase inillumination would undoubtedly have been beneficial since Arthur (2)found that where light of the same composition as sunlight was re-duced to 35 per cent of full sunlight tomato plants thrived best.Assuming 10,000 foot-candles as a value for full sunlight, then anillumination of 3,500 foot-candles would be the optimum illuminationfor tomatoes. In these experiments the higher estimated intensity was1,966 foot-candles, approximately half their optimum intensity.The general form of the plants grown under the near infra-redradiation was somewhat characteristic of plants grown under shadeconditions in that the internodes were long. However, the leaveswere not small as might be expected for shade conditions. Thewater requirement was also lower than that of the plants receivingonly visible radiation. This point is rather interesting because shadingis usually considered an environmental factor increasing the waterrequirement of plants. Thus, some general growth habits of the plantsexposed to the near infra-red radiation are common to plants grownunder shade conditions and others to those grown under normallight conditions.Although the dry weight production was greater for plants ex-posed to the infra-red radiation, these plants were distinctly lessgreen than those receiving only the visible wave lengths. In thehigher intensity of the infra-red the lower leaves were rather yellow.This evident destruction of chlorophyll in the near infra-red regionis extremely interesting. Although considerable work has been doneon growing plants in different colored lights, many of the early re-sults are questionable because of inadequate light filters and a lackof suitable measuring devices for evaluating the intensity factors.In recent years many of these difficulties have been overcome.
12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 87Light within certain wave length and intensity Hmits is generallyconsidered essential to chlorophyll formation, although it is true thatcertain pine seedlings and a few algae become green in darkness.As early as 1874 Wiesner (21) found that chlorophyll was formedin plants when illuminated by light passed through solutions ofpotassium bichromate and copper sulphate. These filters divided thevisible spectrum into two parts. He also showed that no greeningoccurred in the nonluminous heat rays.Sayre (15) studied the development of chlorophyll in seedlings ofseveral varieties of plants by growing them under Corning glass rayfilters and noting the relative greenness as compared with seedlingsgrown in full daylight. No greening was observed in wave lengthslonger than 6,800 A. In the visible spectrum he found that for ap-proximately equal energy values the red wave lengths were moreeffective for the development of chlorophyll than the green and thegreen more effective than the blue. The effectiveness apparently in-creased with increasing wave length up to 6,800 A, where it endedabruptly.Shirley (16) working with several types of plants grown in thespectral greenhouses at the Boyce Thompson Institute for PlantResearch found an increase in chlorophyll concentration with de-creasing intensity to a point so low as to hazard the health of theplant. At approximately 10 per cent of full sunlight intensity thechlorophyll content was practically the same for wave lengths 3,890-7,200, 3,740-5,850 and 4,720-7,200 A.Plants grown at high altitudes were found by Henrici (9) to con-tain less chlorophyll than similar ones grown at lower altitudes. Asnoted by Spoehr (17) "this is presumably due to the greaterintensity of light at higher altitudes. However, whether the lowerchlorophyll-content of plants grown under high illumination intensitycan be directly ascribed to the destructive action of such light (espe-cially the red-yellow rays) on chlorophyll, does not seem entirelyestablished."Tomato plants grown under ordinary greenhouse conditions andthen placed under continuous artificial illumination were found byGuthrie (8) to show a marked decrease in their chlorophyll content ina few days. The leaves turned yellow and later showed necrotic areas.By analysis the chlorophyll decrease was greater on the dry-weightthan the fresh-weight basis, due to a very large increase in carbo-hydrates. It is interesting to note that this author found a consistentlowering of the chlorophyll a/chlorophyll b ratio. Both a and b de-creased under the effect of the light, but a decreased faster.
NO. 14 EFFECTS OF INFRA-RED ON PLANTS JOHNSTON I3
If radiation within certain wave length and intensity limits isnecessary for the formation of chlorophyll and if, as appears probable,other radiation limits are destructive either directly or indirectly,then the amount of chlorophyll present in a leaf at a given time isthe resultant of these two processes of production and destruction.According to Sayre, as noted above, the effectiveness of the wavelengths apparently increases up to 6,800 A., where it ends abruptly.In earlier experiments it appears that no distinction was made be-tween the near and far infra-red, so that definite conclusions cannotbe drawn. From the present experiments it would appear that thenear infra-red has a decided destructive action on chlorophyll, evengreat enough to surpass its rate of formation in the presence of wave-lengths shorter than 6,800 A. It should be remembered, however,that these tentative conclusions are based on the appearance of theleaves. Before definite conclusions can be drawn the experimentsshould be repeated and chlorophyll determinations made.From the experiments of Arthur (i) on the production of pigmentin apples it appears that the near infra-red radiation alone or in thepresence of visible light has a marked detrimental effect on apples.Under these rays a typical wrinkled, necrotic area soon develops. Inhis work with tomato plants Arthur found that injury occurred withthe use of continuous illumination even as low as 150 foot-candles.The fact that the rate of injury was greatly decreased where halfsunlight and half artificial light was used emphasizes the necessityfor a more thorough investigation of light sources whose distribu-tions differ from that obtained with the Mazda lamp.One point should not be lost sight of, namely, that in the region ofthe strongest chlorophyll absorption bands the plants grown in thedistribution including the infra-red receive some three times greaterintensity of radiation. This very likely in large measure accounts forthe greater increase in dry weight exhibited by the plants grownunder this distribution. It is furthermore likely that the higherinternal temperatures produced by the more penetrating near infra-red would account to some extent for other differences exhibited.In a future experiment it is hoped to compare two distributionsin which the radiation in this region is approximately equalized. Forthis purpose it will be necessary to secure heat-absorbing filters whichcut off at longer wave lengths.CONCLUSIONSThe tomato plants that received both visible and excessive nearinfra-red radiation under the artificial conditions of these experiments
14 SMITHSONIAN^ MISCELLANEOUS COLLECTIONS VOL. 87
showed some general growth habits common to both normal andshade-grown plants. The internodes were larger, the leaves larger,and the water requirement less than in plants grown under thevisible radiation alone.A marked decrease in chlorophyll occurred in the leaves of thetomato plants grown under the full visible and infra-red range ofwave lengths. A distinct yellowing and death was noted in extremecases. It appears that, if not actually destructive, this infra-red regionof the spectrum is of little or no benefit to chlorophyll formation.It would appear that normal growth of the tomato plant can beobtained under artificial light conditions where the infra-red is cutoff and the intensity great enough.From a review of the literature and from the results obtained inthese experiments with the tomato plant it appears that the nearinfra-red region of the spectrum is of considerable biologicalimportance.Furthermore, experiments comparing the effects of different por-tions of the visible region must be scrutinized for the possiblepresence of different amounts of near infra-red.LITERATURE CITED(1) Arthur, John M.1932. Red pigment production in apples by means of artificial lightsources. Contrib. Boyce Thompson Inst., vol. 4, pp. 1-18.(2) Arthur, John" M.1932. Some effects of visible and invisible radiation. (Abstract) Torreya,vol. 32, pp. 107-108.(3) Arthur, John M. ; Guthrie, John D. ; and Newell, John M.1930. Some effects of artificial climates on the growth and chemicalcomposition of plants. Amer. Journ. Bot., vol. 17, pp. 416-482.(4) Atkinson, Geo. F.1893. Oedema of the tomato. Cornell Agric. Exp. Sta. Bull. 53,pp. 101-128.(5) Brackett, F. S., and Johnston, Earl S.1932. The functions of radiation in the physiology of plants. I. Generalmethods and apparatus. Smithsonian Misc. Coll., vol. 87, no. 13,pp. I-IO, I pi.(6) BuRK, Dean; Lineweaver, Hans; and Horner, C. Kenneth.1932. Iron in relation to the stimulation of growth by humic acid. SoilSci., vol. 33, pp. 413-452.(7) Funke, G. L.1931. On the influence of light of different wave-lengths on the growthof plants. Recueil des travaux bot. Neerlandais., vol. 28, pp.431-485-(8) Guthrie, John D.1929. Effect of environmental conditions on the chlorophyll pigments.Amer. Journ. Bot., vol. 16, pp. 716-746.
NO. 14 EFFECTS OF INFRA-RED ON PLANTS—JOHNSTON I5(9) Henrici, Marguerite.1918. Chlorophyllgehalt unci Kohlensaureassiniilation bei Alpen- undEbenenpflanzen. Verh. Naturforsch. Ges. Basel, vol. 30, pp.43-136.(10) Meyer, L.1929. Die Tomate, ein empfindlicher und schneller Indikator fiir Phos-phorsauremangel des Bodens. Fortschr. Landwirtsch., vol. 4,pp. 684-693.(11) Orton, C. R., and McKinney, W. H., Jr.1918. Notes on some tomato diseases. Ann. Rep. Pennsylvania Agric.Exp. Sta. 1915-16, pp. 285-291.(12) Johnston, Earl S., and Hoagland, D. R.1929. Minimum potassium level required by tomato plants grown inwater cultures. Soil Sci., vol. 27, pp. 89-106.(13) Johnston, Earl S., and Dore, W. H.1929. The influence of boron on the chemical composition and growthof the tomato plant. Plant Physiol., vol. 4, pp. 31-62.(14) Johnston, Earl S., and Fisher, Paul L.1930. The essential nature of boron to the growth and fruiting of thetomato. Plant Physiol., vol. 5, pp. 387-392.(15) Sayre, J. D.1928. The development of chlorophyll in seedlings in different rangesof wave lengths of light. Plant Physiol., vol. 3, pp. ^\-^^.(16) Shirley, Hardy L.1929. The influence of light intensity and light quality upon the growthof plants. Amer. Journ. Bot., vol. 16, pp. 354-390.(17) Spoehr, H. a.1926. Photosynthesis. The Chemical Catalog Co., Inc., New York.(18) Teodoresco, E. C.1899. Influence des diverscs radiations lumineses sur la forme et lastructure des plantes. Ann. Sci. Nat. Botanique 8^ ser., vol. 10,pp. 141-162.(19) Teodoresco, E. C.1929. Observations sur la croissance des plantes aux lumieres de di-verses longueurs d'onde. Ann. Sci. Nat. Botanique 10"" sen,vol. II, pp. 201-336.(20) Waixace, R. H.1928. Long time experiments with plants in closed containers. Bull.Torrey Bot. Club, vol. 55, pp. 305-314-(21) Wiesner, J.1874. Untersuchungen iiber die Beziehungen des Lichtes zum Chlo-rophyll. Sitzungsber. d. k. Akad. d. Wiss., vol. 69, pp. 327-385.

SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 87, NO. 14, PL. 1
GENERAL VIEW OF PUANT GROWTH CHAMBERS AND EQUIPMENT FOR^^^^ ^^ ^^p^^, ^, ENTAU CONDITIONS
SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 87, NO. 14, PL. 2
APPEARANCE OF TOMATO PLANT AFFECTED WiTH OEDEMA BROUGH"ABOUT BY Poor ventilation
SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 87, NO. 14, PL. 3
^3ip|r
5 6Appearance of the Six Groups of Tomato Plants AfterWeeks of GrowthLow light intensity:X'isible plus near infra-red iX'isible only -2Ili^;h light intensity;\ isihle plus near infra-red 4Visible only 3Natural illiiniiiiation
:
In west window of tower 5In north window of laboratory 6
Iu<llJ
(TILuir
uh<H
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