358 THE INDUCTIONS OF BIOLOGY. 



hundred thousand. And then each cluster of biophors com- 

 posing a determinant has to find its way to the place where 

 there is to be formed the part it represents. 



Here it is needless to specify the modifications of these 

 hypotheses espoused by various biologists — all of them assum- 

 ing that the structural traits of each species are expressed 

 in certain units intermediate between morphological units and 

 chemical units. 



§ 97&. A true theory of heredity must be one which recog- 

 nizes the relevant phenomena displayed by all classes of 

 organism. We cannot assume two kinds of heredity, one 

 for plants and another for animals. Hence a theory of 

 heredity may be first tested by observing whether it is equally 

 applicable to both kingdoms of living things. Genesis, he- 

 redity, and variation, as seen in plants, are simpler and more 

 accessible than as seen in animals. Let us then note what 

 these imply. 



Already in § 77 I have illustrated the power which some 

 plants possess of developing new individuals from mere frag- 

 ments of leaves and even from detached scales. Striking 

 as are the facts there instanced, they are scarcely more 

 significant than some which are familiar. The formation of 

 cauline buds, presently growing into shoots, shows us a kind 

 of inheritance which a true theory must explain. As de- 

 scribed by Kerner, such buds arise in Pimpernel, Toad-flax, 

 etc., below the seed-leaves, even while yet there are no axils 

 in which buds usually grow; and in many plants they arise 

 from intermediate places on the stem: that is, without defi- 

 nite relations to pre-existing structures. How fortuitous 

 is their origin is shown when a branch is induced to bud by 

 keeping it wrapped round with a wet cloth. Even still better 

 proved is the absence of any relation between cauline buds 

 and normal germs by the frequent growth of them out of 

 " callus " — ^the tissue which spreads over wounds and the cut 

 ends of branches. It is not easy to reconcile these facts 



