Ch. IV. 7] 



GROWTH OF PLAXTS 



159 



clearly that most plants, 

 when temperature is the 

 same, grow faster at night 

 than in da_\-time : and this 

 fact is famiUar to garden- 

 ers. This greater growth 

 at night, however, is chiefly 

 a result of the fall in tran- 

 spirationwhichaccompanies 

 darkness, but secondarily 

 there seems also involved 

 some release from a direct 

 check imposed upon growth 

 by very bright hght. In 

 such a case the light is sup- 

 posed to act through the 

 unfavorable chemical influ- 

 ence of the blue rays upon 

 the lining 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 httle 

 hght, 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 gro-nth (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 i. a. in darkness : b, in i 

 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 dr\" weight, and the 

 plant ultimately dies of starvation. 

 (From Duggar.) 



