36 PROOFS OF HEREDITY [CHAP. 



then, he argued, the plant might perhaps be able 

 to complete the leaves by filling in the inter- 

 stices between the " ribs," or, as we call it, the 

 " skeleton " of the leaf. 



He took a plant (Proserpinaca palustris, fig. 8 

 of the United States we do not possess it, 

 but it is allied to our Mare's tail) which bears 

 complete leaves out of water, but dissected ones 

 below it. He began his experiments with a 

 saturated atmosphere. This was quite sufficient 

 to check the development of the leaves, so that, 

 although in air, the dissected type was com- 

 menced ; but with regard to the leaves on the 

 submerged part of the stem, all the new leaves 

 produced under the water holding nutritive salts 

 in solution were full sized. 1 



Hence the proof is complete; that such 

 structures, namely, spines in drought, and fennel- 

 like leaves under water are the actual results 

 of the responsive power of the plant, bringing 

 about new and adaptive structures, under the 

 influences of the direct action of changed con- 

 ditions of life. 



But these experiments carry us further. 

 They prove the contrary to what Dr Wallace 

 maintains, that "the transmission of the modi- 

 fications of individuals due to ... climate, food, 

 or other external agencies, has no valid evidence," 

 for having settled the point that the above 



1 Bot. Gaz. } vol. xxxiv., p. 93. 



