316 GROWTH OF PLANTS 



of methods of culture the reader is referred to the original article. The 

 plants numbered 6, in Fig. 129, were grown outside. The experiment 

 was started August 26 but in some cases the plants had been growing for 

 some time before they were placed in the spectral houses. The tomatoes 

 were 31 days old when they were placed in the greenhouses on August 26. 

 Fig. 129 shows the growth of tomato, four o'clock, and soybean grown in 

 the five spectral houses and outside (6). The growth in 6 was durmg Sep- 

 tember for soybean and during September and October for four o'clock 

 and tomato. This means, of course, that the environmental conditions 

 for 6 were very different from those of the spectral greenhouses. All three of 

 these plants showed normal sturdy growth in houses 1, 2, and 3; that is, 

 normal growth and growth of about equal stature occurred in all houses 

 where the full range of the visible spectrum was transmitted in spite of 

 there bemg considerable variation in the percentage transmitted in the 

 different regions of the spectrum, as shown in Fig. 128 and Table 34. On 

 the other hand, all three of these plants show spindly growth in houses 4 

 and 5. This is especially marked in house 5, w^here all the violet, blue, and 

 much of the shorter green are removed and less marked for 4, except in the 

 case of soybean, where the violet and the shorter blue are removed. The 

 soybean takes on the character of a twiner in both 4 and 5. 



Fig. 130 shows Sudan grass and sunflower {Helianihus cucumerifolius) 

 gromng in the five spectral greenhouses for 76 days, and carrot for 139 days. 

 All the plants show normal development in houses 1 to 3 in which a great 

 portion of all the visible rays are transmitted. Also in all these houses 

 Sudan grass and the sunflower were setting flowers in 76 days. In houses 4 

 and 5 the Sudan grass showed much less growth than in houses 1 to 3 but 

 the growth was equal in houses 4 and 5. The sunflower showed much less 

 gro\vth in 4 than in 1 to 3, and very little growth in 5. Neither Sudan grass 

 nor sunflower flowered in houses 4 and 5. The carrot shows least growth 

 in house 5, somewhat more in 4, and decidedly more in houses 1 to 3. 



The author ~'^ summarizes his results on the effect of different portions of 

 the solar spectrum as follows, with minor modifications. When plants were 

 gro\vn in daylight from which all wave lengths shorter than 529 mju were 

 eliminated, they developed the following characteristics as compared with 

 plants grown in the entire spectrum of daylight, (a) An increased rate of 

 elongation of the stem of all species during the first two or three weeks' 

 growth; a greater final height in soybeans, tomatoes, four o'clocks, and 

 coleus, but a decided decrease in height in sunflowers, petunia, buckwheat, 

 and Sudan grass. (6) A considerable decrease in thickness of stems, (c) A 

 reduction in the number of branches or side shoots, {d) A general curling or 

 rollmg of leaves, (e) Good development of chlorophyll, but a reduction in 

 anthocyanin of leaves and flowers. (/) Less differentiation of stem and leaf 

 tissues, less compact and thinner-walled cells, and a reduction in strengthen- 

 ing tissues, {g) Considerable delay in time of flowering and a reduction in 

 the number of flowers produced. Qi) Very weak development of seeds, 



