406 



Heterococcales 



Botryococcus is the most important genus of the family and in some 

 respects it is the most curious genus in the whole of the Chlorophycea?. Its 

 characters long remained obscure and to some extent they are yet very 

 puzzling. It is a difficult Alga to examine with accuracy, with the result 

 that it has been described under several generic names. It occurs as 

 aggregates of botryoidal groups of cells, each group being so closely encased 

 in a peculiar envelope that in the common species Botryococcus Braunii 

 nothing can be seen of the structure of the colony by direct observation 



(fig. 257 A and B). Chodat ('96) has 

 given the most complete account of 

 B. Braunii yet published. Each botryoidal 

 aggregate is rounded although slightly 

 hollowed on its inner side, and it consists 

 of a variable number of cells (20 to 30, or 

 more) arranged as a peripheral layer within 

 the outer envelope (fig. 257 C). The cells 

 are obovate and somewhat elongated, each 

 adult cell being embedded in a sort of 

 gelatinous cupule. The outer envelope, 

 which is doubtless a secretion of the under- 

 lying cells, is of a most irregular character, 

 being folded, wrinkled and often produced 

 into all manner of irregular lobes, processes 

 and spines. This membrane stains strongly 

 with fuchsin, but with chlor-zinc-iodine 

 there is no colouration. Strand-like con- 

 tinuations of the membrane join together 

 the various botryoidal groups of the 

 colony. 



Each cell contains one cup-shaped 

 chloroplast, but this does not as a rule 

 extend to the outer extremity of the 

 cell. Small granules of starch have been 

 detected in the cells and a variable 

 quantity of oil is produced in each cell. This oil may sometimes pass 

 out of the cells, in which case it adheres to the botryoidal groups and 

 their connecting strands and adds to the general obscurity of the structure 

 of the colony. In the late summer and autumn the whole colony may 

 assume a brick-red colour owing to the formation of a pigment which 

 is dissolved in the oil. The cells multiply exclusively by longitudinal 

 division. 



No motile state is known in any of the Botryococcacese. 



Fig. 257. Botryococcus Braunii Kiitz. 



A, outline of medium-sized colony; 



B, smaller colony; C, part of single 

 botryoidal group in section to show the 

 cells within the outer envelope ; D, a 

 colony from which many cells have been 

 extruded by pressure. All x 450. 



