206 THE GKRM-PLASM 



that is to say, it occurs in response to definite external influences. 

 It would not, however, only take place in those parts of the 

 plant which might be assumed to be specially adapted for this 

 capacity, but might also occur in those in which adaptation is 

 out of the question. We are therefore compelled to assume that 

 ))iost, if not all, of the cells contain all the prhnary constituents 

 of the species in a latent condition. 



I will first discuss the manner in which de Vries applies mv 

 hypothesis of the germ-tracks to the case of plants, and the con- 

 clusions at which he has arrived and has illustrated by describing 

 a number of genealogical trees representing the various series of 

 cells in plants. 



De Vries draws a distinction between ' primary ' and ' accessory ' 

 germ-tracks. The former correspond to the germ-tracks I have 

 already assumed : that is to say. to those cell-series which nor- 

 mally lead from the fertilised egg-cell to the new germ-cells (ova, 

 spermatozoa, pollen-grains). By 'accessory germ-tracks' are 

 meant those cell-series which lead to germ-cells ' through ad- 

 ventitious buds.' These accessory germ-tracks are, accordinsf 

 to de Vries, absent in the higher animals, but are of common 

 occurrence amongst plants, and I am accused of not having 

 taken them sufficiently into account. The 'accessory germ- 

 tracks." if I understand the term aright, are regular germ-tracks, 

 which do not, however, always come into use. In many of the 

 lower plants, such as mosses and fungi, 'almost all of the cells 

 may develop into new individuals ; " and in the higher plants, 

 buds, from which entire plants possessing germ-cells may arise, 

 can. under certain circumstances, be formed at any rate from 

 certain kinds of tissue, which may consist of young (meristematic) 

 cells or indeed even of full-grown cells. 



Let us first consider the ' primary germ-tracks.' De Vries 

 thinks that their behaviour is essentiallv different in the hisher 

 animals and in plants : in the former, the genealogical tree of the 

 cells of the germ-track ' is straight, and only slightly branched at the 

 apex,' while in the higher plants • the branches are so numerous 

 and subdivided from the base upwards that they frequently over- 

 top the main stem ; or, more accurately, the main stem is hardly 

 recognisable.' No objection can certainly be raised to this state- 

 ment, which we may illustrate by a blossoming apple tree, in 

 which the blossoms which crown the top may be taken as cor- 

 responding to the germ-cells. But how is this difference to be 



