CH. IV, 7] 



GROWTH OF PLANTS 



159 



clearly that most plants, 

 when temperature is the 

 same, grow faster at night 

 than in daytime ; and this 

 fact is familiar to garden- 

 ers. This greater growth 

 at night, however, is chiefly 

 a result of the fall in tran- 

 spiration which accompanies 

 darkness, but secondarily 

 there seems also involved 

 some release from a direct 

 check imposed upon growth 

 by very bright light. In 

 such a case the light is sup- 

 posed to act through the 

 unfavorable chemical influ- 

 ence of the blue rays upon 

 the living protoplasm, an 

 action which, in forms like 

 the Bacteria, where the pro- 

 toplasm is, unshielded by 

 chlorophyll or other color- 

 ing matters, makes strong 

 light actually germicidal. 

 But if plants are continu- 

 ously exposed to too little 

 light, they tend to "draw," 

 as the gardeners say; that 

 is, they become pale, in 

 obvious partial starvation, 

 and elongate greatly at ex- 

 pense of other growth (Fig. 

 111). This elongation has 

 been commonly supposed 

 to represent an adaptive 



FIG. 111. Effect of different in- 

 tensities of light upon the growth of 

 Peas ; X . a, in darkness ; b, in % 

 light ; c, in full light. While for a time 

 the growth in darkness is much the 

 greater, the extra bulk is chiefly water, 

 there is loss of dry weight, and the 

 plant ultimately dies of starvation. 

 (From Duggar.) 



