CONTROLLED ENVIRONMENTAL CONDITIONS 325 



sities of light by screening the plants mth one or more layers of cheese- 

 cloth or muslin in (a) the constant-condition artificial light room, (6) in the 

 spectral glass houses, (c) in ordinary greenhouses, and (d) outdoors. This 

 gives a great variation in both the intensity and quality of the light. The 

 foUomng plants were used in the study: buckwheat, a dwarfed sunflower, 

 Galinsoga, Geiim, redwood, wandering Jew, loblolly pine, hog peanut, 

 tomato, and tobacco. This includes plants commonly growing in shade at 

 least in the early stages, such as redwood, loblolly pine, Galinsoga, and hog 

 peanut, and plants demanding or commonly gro^\ing in high fight intensi- 

 ties, such as the sunflower and buckwheat. 



Fig. 133 shows the growth of redwood under light of various intensities 

 and sources. In the constant-condition artificial fight room the growth was 

 about the same in 330, 240, and 100 foot-candles, ^^^th a great reduction 

 rate in 50 and 30 foot-candles. In the greenhouse good growth was sho^\Tl 

 in 71, 40, and 19 per cent of full sunlight, greatly reduced growth in 8 per 

 cent, and little gro^^'th in 1 per cent of full sunlight; outdoors good growth 

 occurred in 20, 47, and 74 per cent of fuU sun'ight, with sfight dwarfing in 

 stature in 100 per cent full sunlight. For the sunflower, as sho^Mi in Fig. 134, 

 reducing the light in the artificial fight room from 600 to 260 foot-candles 

 caused a great reduction in growth. In the greenhouse, reduction of gro^i:h 

 was evident in 19 per cent of full sunlight, marked in 8 per cent, and com- 

 plete in 1 per cent; and in the open, good growth occurred in aU intensities 

 tried down to 21 per cent of full sunlight, the lowest intensity used. 



Geum gro\\TL in the artificial light room (Fig. 135) showed a gradual reduc- 

 tion in growth as the light intensity feU from 470 to 41 foot-candles. In the 

 latter there Avas very little growth even after 54 days. Sunflower gro\vn in 

 the spectral greenhouses with low but nearly equal intensities, except for 

 house 5, gave much better growth in house 1 (full visible spectrum with 

 ultraviolet excluded) and in house 2 (ultraviolet-transmitting glass) than 

 in the other houses AA^ith onlj'- a part of the visible spectrum. House 3 trans- 

 mitted the blue and violet and cut out all rays longer than 600 m;u; it also 

 greatly dimmed the green and yeUow. The glass on house 4 cut out most of 

 the violet and dimmed the shorter green, but it transmitted a large per- 

 centage of the longer green and yeUow, orange and red. House 5 cut out 

 aU the violet, blue, and shorter green but transmitted a considerable per- 

 centage of the long green and a greater percentage of yeUow, orange, and 

 red. The plants grown in houses 4 and 5 were smaU and spindfing and 

 those in house 3 were short but sturdy. Geum plants grown in the spectral 

 houses were less unfavorably affected by the unbalanced spectrum than 

 sunflower, although there is some evidence that house 5 was unfavorable. 

 Galinsoga grown in the spectral greenhouses behaved more like the sun- 

 flower, except that the growth in height is considerable in houses 4 and 5. 



The author concludes that light needed for the survival of all the plants 

 studied is very low, less than 40 foot-candles, except for the sunflower, 

 which needs much higher intensities. Redwood and loblolly pine survive 



