MULTIPLICATION BY GEMMATION 1 65 



next division of the lower of the two daughter-cells, however, 

 separates the determinants into two dissimilar groups, for it re- 

 sults in the production of an upper biconcave ' nodal cell.' from 

 which the leaves (d\ b^\ <^'", /;"'). the lateral shoot {k), and the 

 sexual organs {a and o), will subsequently arise; and of a lower 

 biconvex cell, which does not undergo further division, but only 

 grows considerably in length, so as to form a segment of the 

 main axis (/', /", /'". /'^). The idioplasm of this • internodal 

 cell ' does not therefore undergo further disintegration ; the nodal 

 cell, however, divides vertically, so as to form cells which, since 

 they give rise to other parts of the shoot, must contain various 

 groups of determinants. Thus a comparison of the younger 

 with the older segments of the shoot, shows that the outer of the 

 five nodal cells in the figure gives rise to a whole leaf, together 

 with the sexual organs, the inner ones forming the actual node. 

 The division of the outer cell is accompanied by constant though 

 usually unimportant changes as regards its idioplasm : a glance 

 at the structure of the leaf, in which similar segments are 

 repeated many times over, will make this evident. If we now 

 leave out of consideration the accessory idioplasm which is 

 present in the cells along with the primary idioplasm, it will be 

 seen that the distribution of the group of determinants derived 

 from the apical cell must simply take place so as to result in each 

 cell, as it is formed, receiving that group of determinants only, 

 the individual constituents of which are required by its successors 

 for the control of the individual cells. We must therefore sup- 

 pose that the internodal cells of the stem only contain their own 

 specific idioplasm, composed of • internodal determinants,' for 

 they do not give rise to any other structures. The primary 

 nodal cell, on the other hand, must contain an entire group of 

 determinants, as it gives rise to a number of cells which have 

 various forms and perform various functions. 



Although the cells of plants are often apparently very much 

 alike, and no essential difference can be observed between them, 

 such a difference must exist if the origin of the specific leaf, 

 stem, and reproductive organs can be proved theoretically at 

 all. For the origin of these structures can only be explained, at 

 any rate in principle, by supposing that each of these centres of 

 vitality is controlled by a specific idioplasm ; that is, by a deter- 

 minant which differs in some way or other from those in the 

 other cells. 



