Fig. 148 Botryococcus hraunii. A, colony ( x 300). B, portion of 

 colony showing cells in their mucilage envelope. C, two cells en- 

 closed in the parent cup. D, portion of colony enlarged ( x 780). E, 

 two cells arranged diagrammatically to show structure, c = cup, cc = 

 cell cap, cw =cell wall, pc = parent cell, pm =pectic mucilage, pt = 

 parent thimble, r= thimble. (A, after Smith; B, C, after Fritsch; 



D, E, after Blackburn.) 



firmation. Normally reproduction is secured by means of aplano- 

 spores, of which two to four are 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 Uving Botryococcus Braunii. 



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

 149. 



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

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

 cytoplasm where it is associated with numerous discoid chloro- 

 plasts. A new membrane is formed internally and then the old one 

 ruptures, but as the latter may still persist outside one can often see 

 what appears to be a multi-layered sheath. Reproduction can take 

 place by means of zoosporic swarmers but these may be replaced 

 by aplanospores, whilst resting cysts are also recorded. Although 

 most abundant in the warmer oceans, especially during the winter 

 months, its life history is as yet only imperfectly known. 



261 



