388 



GZdoyoniales 



On the germination of the zoogonidium in Bulbochxte there is formed a basal cell 

 similar to the rhizoidal basal cell in many species of (Edogonium. This remains the only 

 active cell in the primary axis and is therefore the only one capable of division. The first 

 division of the basal cell is of a simple type, without any ring-formation. The upper part 

 of the wall separates by a circular split and, as the new cell grows upwards, the detached 

 portion is pushed to one side in a lid-like manner (fig. 246 J). This first new cell grows 

 out to form a long tubular bristle with a swollen bulb-like base (fig. 246 J br}. Subsequent 

 divisions are normal, with ring-formations, and each new cell is intercalated between the 

 basal cell and the next one above. Thus the upper cell of a branch is the oldest one. 

 Any cell of the main axis, except the basal cell, is a potential basal cell of a side branch, 

 and the branches grow like the main axis by the divisions of their respective basal cells. 

 The cells each undergo one division without ring-formation, the new cell breaking through 



the mother-cell-wall laterally at its upper 

 end and forming a tubular bulbous 



^pjaagv ^ bristle (fig. 246 A'). Should the cell then 



sP r9s) & become the basal cell of a branch sub- 



sequent divisions occur with ring-forma- 

 tion and the axis of the branch is 

 deflected in the direction of the axis of 

 the bristle. The cells of lateral branches 

 of the first order become the basal cells 

 of branches of the second order and 

 so on. 



Asexual reproduction takes 

 place by means of zoogonidia of 

 comparatively large size, which are 

 formed singly from the vegetative 

 cells. Very good and reliable 

 accounts of the liberation of the 

 zoogonidia were given by Braun 

 ('49) and by Pringsheim ('58), and 

 since that time some further details 

 have been added. In the vegetative 

 cell about to become a zoogoni- 

 dangium the protoplast undergoes 

 a rejuvenescence and gradually 

 contracts away from the wall. The 

 cell-wall then splits transversely 

 at or near the upper end of the 

 cell and the rejuvenated proto- 

 plast, enclosed in a delicate hyaline 

 vesicle, emerges from the opening 

 (fig. 243 A and B). At first the 



emerging zoogonidium is rather irregular in shape, but it quickly becomes 

 rounded (fig. 243 B) and in many cases pyriform (fig. 89). Around its 



Fig. 242. Bulbochsete minuta W. & G. S. West, 

 x 453. and, androgonidangiuni ; n, naunan- 

 drium or dwarf male. 



