THE FORMATION OF GERM-CELLS 20g 



self-evident that each apical cell contains the germ-substance of 

 the ovum, because in plants all growth takes place from the 

 growing point and originates in the apical cells, which are 

 derived directly from the egg-cell. 



This, however, is at any rate only self-evident in the case of 

 the first apical cell of the main shoot, and is certainly not so in 

 that of the lateral shoots, which are, indeed, only derived indi- 

 rectly from the former. All the cells of a plant are undoubtedly 

 descended in a direct line from the ovum ; but this fact does not 

 imply that they must all give rise to apical cells or must all con- 

 tain germ-plasm, nor does it in any way explain the fact that 

 only relatively few of them can become germ-cells and the rest 

 cannot. These were the very facts which the hypothesis of the 

 continuity of the germ-plasm was intended to make compre- 

 hensible, to some slight extent at any rate. The origin of a cell 

 from the ovum gives no clue to its nature ; and. as de Vries him- 

 self says, the entire description in detail of the cell-series leading 

 from the ovum to the first apical cell, although very interesting 

 in itself, gives us no information as to the origin of the germ- 

 substance present in certain parts of the plant-body. I do not 

 understand therefore how de Vries can look upon the fact of the 

 existence of these cell-series as constituting in itself an important 

 explanation of the problem, without attempting to explain it 

 further. It seems to me that the cell-series can only be of any 

 explanatory value when they are regarded as germ-tracks in the 

 sense in which I use the term, — that is to say, as those series 

 through which the germ-substance is transmitted from the egg- 

 cell to the remotest parts of the plant. 



I must say that it seemed to me to be a somewhat crude idea 

 to suppose that the same kind of idioplasm is contained in all 

 the cells of the germ-track, including the apical cell, and that it 

 is equivalent to 'germ-substance.' Why do not the apical cells 

 in the sterile shoots of the horse-tail give rise to germ-cells, 

 while those of the fertile shoots do so? This must be due to a 

 difference in the idioplasm of the apical cells of these shoots. And 

 although structures bearing germ-cells may become developed 

 from the apical cell of a fertile shoot of the plant, all the cells of 

 the latter do not nevertheless give rise to germ-cells : only certain 

 cell-series lead from the apical cell to the new germ-cell, and 

 these are the cells of the germ-track which contain germ-plasm! 

 The process of the formation of a shoot from an apical cell is 



