The Freshwater Algae of Africa. 499 



cellulae maternae in apice aperitur. Innovatione hac cellula gradatim 

 a basi discedit. Divisio cellularum oblique plerumque in duas partes 

 fit, et turn membrana cellulae maternae aperitur; una e cellulis 

 filialibus sursum proeedit et hiatui cellulae maternae se adjungit, 

 altera cellula filialis plerumque in basi cellulae maternae manet. 

 Coloniae parum ramosae et simplices sunt. Propagatio ? (zoosporas 

 divisione succesiva magnae cellulae in partes plures probabile est). 



Dimensiones cellularum maternarum : 86 x 9, 42 x 115, 45 x 9, 

 51 x 12, 54 x 10-5, 56 x 12, 60 x 12, 67 x 105 fi. Cellulae filiales 

 (ubi plures efficiuntur; zoosporae ?) : 18 x 6, 21 x 7-5 /x. 

 Sample 19. 



The characteristic feature of this species is the abundant and 

 repeated occurrence of rejuvenescence. The initial cell of a colony 

 is here attached to its substratum by a broad pad of mucilage 

 (Fig. 4, a, e,f, g). In this species this does not appear to be derived 

 from a thickening of the membrane, but rather to be an excretion 

 from the lower end of the cell. The same seems to be true of the 

 secondary points of attachment (Fig. 4, a,/ ), which appear as diffuse 

 mucilage-areas, well seen after staining with haematoxylin. There is 

 no noticeable thickening of the membrane at the ends of the very 

 elongated cells. 



The process of rejuvenescence appears to set in at a very early 

 stage and to take place as follows : The cell undergoes more or less 

 marked elongation, during which the protoplast gradually recedes 

 from the lower end, while maintaining a close connection with the 

 upper end. It appears that the space, which thus arises in the lower 

 part of the cell, is empty, since attempts to disclose the presence of 

 mucilage, by employing such stains as methyl blue, gave no result. 

 This point should be easy to settle with fresh material. If the area at 

 the lower end of the cell is really empty, we have a rather interesting 

 case of growth of the cell, without any accompanying increase in the 

 size of the protoplast. The extent of the space wdiich thus develops 

 is very variable ; sometimes the protoplast only shifts upwards a little 

 way before further events ensue (Fig. 4, a, c, y) ; in other eases, 

 however, the cell may almost double its length before the process 

 comes to a stop (Fig. 4, b). 



When the elongation of the cell has reached its end, a new 

 membrane appears around the contents aud the original wall of the 

 nmther-cell breaks apically (Fig. 4). From Figs. 4. c and g, the 

 frequency of this process of rejuvenescence can lie gauged, and it will 

 lie realised that, by tins process, the protoplast of the original cell 

 gets carried away from the point of attachment, with more or less 



35 



