78 Morphology BOOK i 



are hereditary though still capable of varying under changes 

 of conditions. 



It remains an interesting question how far the heredity of 

 these forms in detail is the result of long acting conditions 

 affecting in succession the protoplasm of countless genera- 

 tions, and how far of inherent tendency superior to their action. 



The advocates of these physiological speculations found 

 themselves obliged, however, to accept the categories of 

 stem and leaf as existing in the higher plants. Though 

 they differed from the morphologists in their conception 

 of them, and denied that they are fundamental, they 

 admitted their convenience for descriptive purposes and 

 made no attempt to introduce new terms which should 

 indicate dissent from the position of the older writers. 

 Their position was consequently not so different as at first 

 it seemed to be from that of the advocates of metamor- 

 phosis as stated by Wolff and Goethe. The difference was 

 rather as to the origin of, than as to the changes possible 

 in, the outgrowths universally called leaves. It was possible 

 to accept a physiological basis of form, and yet to admit 

 that these, or any outgrowths, could be made to assume 

 different forms under the stress of physiological need. This 

 aspect of the theory of metamorphosis differs but slightly 

 from that put forward by Sachs in the Lehrbuch, in the 

 words, ' Metamorphosis is the varied development of 

 members of the same morphological significance resulting 

 from their adaptation to definite functions.' It does not 

 seem very clear what importance Sachs attached to the 

 words ' morphological significance ', for he goes on to say 

 ' The conceptions of stem, leaf, root, trichome, as at present 

 employed in botany, result from the consideration of highly- 

 developed plants, the different members of which actually 

 present considerable diversities, from a purely formal point 

 of view ; l . . . absolute distinctions between thallomes and 



1 The italics are the Author's. 



