XANTHOPHYCEAE 



115 



though the sheath is so predominant nevertheless its origin is not 

 clearly known. The cells multiply by longitudinal division, whilst 

 asexual reproduction by means of zoospores has also been recorded 

 though it requires confirmation. Normally reproduction is 

 secured by means of aplanospores, of which two to four are 



Fig. 78. Fig. 79. 



Fig. 78. A, Chloramoeba heteromorpha, cyst. B, the same, motile phase. c = 

 chloroplast, « = nucleus, w = vacuole. C, flagellum structure in Monocilia. 

 (After Fritsch.) 



Fig, 79. Botryococciis Braunii. A, colony ( x 300). B, portion of colony showing 

 cells in their mucilage envelope. C, two cells enclosed in the parent cup. D, por- 

 tion of colony enlarged ( x 780). E, two cells arranged diagrammatically to show 

 structure. c = cup, cc = cell cap, cic = ceW wall, /)c = parent cell, pm = pectic 

 mucilage, ^? = parent thimble, f = thimble. (A, after Smith; B, C, after Fritsch; 

 D, E, after Blackburn.) 



produced in each cell. The colonies decay very slowly, and one of 

 the principal interests of the genus is the recent discovery that 

 boghead coal is composed very largely of this organism, whilst the 

 fossil genera Pila and Reinschia hardly differ from the living 

 Botryococcus Braunii. 



Halosphaeraceae : Halosphaera (halo^ salt; sphaera, sphere). Fig. 

 80. 



The large, free-floating spherical cells possess one nucleus which 

 is suspended either in the central vacuole or else in the parietal 



8-2 



