178 NATURAL SCIENCE. 



MAS", 



experiment how easily the anatomy of plants can be affected by their 

 environment ; and as long as the latter is constant, so are the 

 characters of the plant constant and hereditary. 



Dr. Weismann, however, would attribute such susceptibilities 

 to an assumed " predisposition," instead of regarding it as a universal 

 property of protoplasm to respond to external influences. One 

 cannot disprove the existence of such a predisposition, but it seems 

 unnecessary to assume it, when probabilities are accumulative on 

 the other side, which render it entirely unnecessary. 



As an instance of a natural change of structure and habit, I 

 have often found Ranunculus heteyophyllus growing on mud after the 

 water has dried up. As in the case of the normally submerged plant, 

 finely dissected foliage had still grown, but altered in character. The 

 segments had become rigid, broader, and with stomata. The leaves 

 were all erect, forming a sort of green " pile," and perfectly adapted 

 to aerial conditions. Such may, perhaps, be compared to the Mud- 

 fish, which can breathe in both water and air. In another case 

 the plants became prostrate, rooted at the joints, formed no more 

 dissected leaves, and were in all respects similar to a form of R. 

 hederaceus. 



Similar alterations occur in terrestrial plants raised by seed sown 

 in pots, collected from the aquatic form. The cotyledons at once 

 appear of a different character. Then, the first leaves are dissected, 

 but " aerial," the subsequent ones being of the " floating " type ; as 

 if the plant had reached the surface of some imaginary water ! This 

 illustrates, therefore, very well what is a universal feature, viz., the 

 combination of hereditary characters in conjunction with direct 

 adaptations to a new environment. If the above plants be trans- 

 ferred to water, the "aerial" dissected leaves die, and "aquatic" 

 dissected leaves are immediately developed. 



As Dr. Weismann includes "chmate" as one of the forces acting 

 on the individual which may produce " acquired characters," I may 

 add the effects produced by a change from an Alpine to a low-level 

 habitat, as well as from a high to a low latitude. It is well-known 

 that there are not only plainly visible differences, such as a richer 

 foliage and brighter coloured flowers, in high latitudes and Alpine 

 regions, but the anatomical details of structure of the leaves are very 

 different. 



As in the case of experimental evidence of the effects of water, 

 so in the case of these conditions, M. Bonnier'- has proved by cultiva- 

 tion that when plants are changed from one locality to another, being 

 grown from seed, the vegetable system soon begins to respond to the 

 new chmatic conditions, and assumes the histological characters of 

 the plants normally growing in the same environment. 



12 Bull. Soc. Bot. France. 18S6, p. 467. See also Ann. des Set. Nat. Bot., 1879, and 

 Rev. Gen. Bot., vol. ii., 1891, p. 513 



