212 THE GERM-PLASM 



all parts of the leaf; they are only formed in perfectly definite 

 j'egions, e.g., on the margins of the leaves in Bryophyllum and 

 in the angles between the points of origin of the large veins in 

 Begonia. All the cells of the leaf do not, therefore, as de Vries 

 supposes, possess this capacity, which is limited to perfectly 

 definite though numerous cells. These therefore correspond to 

 somatic cells, quite as much as do those which produce the 

 several cells in the prothallus of a fern, which contain unalter- 

 able germ-plasm in addition to the active somatic idioplasm, 

 the former only becoming active by the influence of particular 

 external influences. 



These conditions may be fulfilled in thousands of other leaves 

 without resulting in the production of young plants. There are 

 indeed a whole series of observations which apparently prove 

 that ' every small fragment of the members of a plant contains 

 the elements from which the whole complex body can be built 

 up, when this fragment is isolated under suitable external condi- 

 tions.' Phenomena of this kind are exhibited by cuttings and 

 adventitious buds which arise on a twig the apex of which has 

 been cut off. In the higher plants, the development of roots on 

 a cutting, or the formation of adventitious buds, does not take 

 place in all parts of the plant, but only in those which contain 

 ^ a number of cambium cells.' These cells alone therefore con- 

 tain accessory idioplasm, w^hich, according to the nature of the 

 stimulus acting on them, renders them capable of growing in a 

 manner which is very different from the normal. There can be 

 very little doubt that the whole of the cambium layer of these 

 plants is endowed with the capacity for reproduction. The only 

 question is, whether this is a result of special adaptation, or 

 only the outcome of the normal constitution of each plant-cell. 



I should still, however, be inclined to consider it as a special 

 adaptation, and will endeavour to state my reasons for this 

 view ; not being a specialist in botany, however, I am unable to 

 deal with the various groups of the vegetable kingdom in such 

 detail as I could wish. 



The question to be decided is, whether each cell was pro- 

 vided with all the specific primary constituents in a latent con- 

 dition at the time when the multicellular plant arose from the 

 unicellular form ; or w^hether, owing to the diversity of the 

 differentiation of the idioplasm, a sharp distinction first arose 

 between the somatic cells and the germ-cells, and the idioplasm 



