132 



Fig. 140. Peyssonnelia (Cru- 



oriella) simulans nov. spec. 



Section throug the.' margin 



of thallus. t. topcell or apical 



cell ; the one row of inferior 



cells constitute the hypothal- 



lus, the ascending, still short 



cellrows, the perithallus. 



(200:1). 



it may be higher (P. (Eup.) simulans), but it is always less high 

 than the apical cell (Fig. 140). 



In a few other species (P. (Eup.) rubra} the topcell or the cells 

 following may be longer than high ; it divides just like the short 



one by an oblique cellwall on its longitu- 

 dinal axis into two segments. The outer 

 one grows until it has reached its for- 

 mer size and then divides again. The in- 

 ner segment will grow too, and may first 

 divide again by a vertical cellwall ; if this 

 is the case, the third or even the fourth 

 cell after repeated division, increases in 

 height and then divides by a hori- 

 zontal wall into two often unequal 

 portions. The inferior one retains the 

 height it had at the moment of divi- 

 sion of the apical cell ; it communicates with its neighbouring 

 hypothallic cells of the same filament through the primary cen- 

 tral pore ; the upper portion is the mother cell of the ascending 

 filaments. I thought at first that these differences in growth of 

 the apical cell might coincide with the branching of the hypo- 

 thallus, but this is not the case. I have found the short, high 

 apical cell in species belonging to the subgenus Eiipeyssonnelia as 

 well as to the subgenus Cruoriella and in both subgenera the 

 longer and less high apical cell. 

 Therefore I consider this character 

 only useful as a specific one, but 

 as a good one, for great as the va- 

 riability of the Peyssonnelia may 

 be, I can not imagine that a top- 

 cell as in Fig. 140 can grow into 

 a topcell like Fig. 144. 



When treating of the Peys- 

 sonnelia of the Siboga Expedition, 

 I hope to be able to give some 

 more details about the growth 



of the apical part of these alga3, but this study is very tedious, 

 for dried specimens have the margin often crumpled or broken 

 off. It is also difficult to get good longitudinal sections and the 

 topcell must be in a growing stage. In old fronds, when their 

 maximum size is reached, the topcells cease growing in radial di- 

 rection but they may still divide in another way and slides made 



- rr 



Fig 141. Peyssonnelia rubra (Grev.) 

 J. Ag. A longitudinal section 

 through margin of thailus. t. top- 

 cell ; p. perithallus; /?. hvpothal- 

 lus; rh. rhizoid. (360:1). 



