Evolution of Structure in Seedlings. 49 



leaves and tendrils are many times larger than in Table I., 

 and they with the whole plant are of a bright green colour, 

 instead of the sickly pale yellow of Table I. : but the light has 

 not developed any new structure ; it has only perfected those 

 which preexisted, and converted other substances into chloro- 

 phyl, which is not an organized body. 



Not only did the plants in the two series present similarities 

 in evolution of structure, but the average weight of dry plant 

 in each was very nearly the same ; for 



mgr. mgr. 



455 of seeds in the dark produced 184 of dry plant, 

 while 455 „ light „ 215 „ 



A comparison of the parts below the ground with those 

 above (both being dried at 212° F.) shows that the proportion 

 of root to total weight of plant was also nearly identical, 

 being 



25 of root for 100 of plant in the dark, and 

 23 „ 100 „ light. 



The close similarity in the evolution of visible structure in 

 the light and in the dark, the small difference in the total 

 weights of the plants grown in the same time in both series, 

 and the close approximation in the proportional weight of root 

 to plant, all justify the conclusion that the growth in darkness 

 and in light closely resemble each other, and that it is proper 

 to reason, as regards the natm*e of the action, from the first to 

 the second. 



Another interesting fact which l^nds support to the opinion 

 that the process of growth in seedlings developed in the dark 

 is very similar to that occurring in those grown in the light, is 

 the character of the excrements thrown out by the roots. It is 

 well known that many plants so poison the soil that the same 

 plants cannot be made to grow therein until the poisonous 

 excretions from the roots of the first crop have been destroyed 

 by oxidation. In the case of peas this poisoning of the soil 

 takes place in a veiy marked manner ; and I have found that in 

 ''^l the pots in which peas have been grown in the dark, the soil is 

 so poisoned by the excrements from the roots that a second 

 I 11 )p fails to sprout. Does it not follow that since, in the two 

 scries with which I experimented, tlie excrements from the 

 roots possessed the same poisoning action, the processes in the 

 jilants from which these excrements arose must have been 

 similar? 



There remains an important argument, concerning which 

 nothing has thus far been said. It is to be derived from the 

 consideration of the rate of growth in the light series during 



Ann. & McHj. N. Hist. Ser. 4. Vol. xi. 4 



