Protococcacece 235 



Sub-family VII. DICTYOSPH.ERIE.E. 



This sub-family contains a few genera the affinities of which 

 are somewhat doubtful. The cells are globose, ovoid, or ellipsoid, 

 and are associated to form more or less indefinite colonies. The 

 colony is often of a fragile nature, the cells being held in position 

 by the persistent old walls of the mother-cells, which sometimes 

 become transformed into definite connecting-threads. A copious 

 mucous investment is present in some, but in others it may be 

 entirely absent. The multiplication is by simple vegetative divi- 

 sion or by the formation of four daughter-cells (autospores) within 

 the wall of the mother-cell, which gradually splits open and permits 

 their escape. Reproduction by biciliated zoogonidia has been 

 observed by Zopf and by Massee 1 in Dictyosphcerium. 



The sub-family is most probably an artificial one and perhaps 

 it should not have a place in the Protococcacese. 



The five following genera are British : 



A. Cells indefinitely disposed. 



* With well-marked, subdichotomous connecting- 



th reads ; chloroplast parietal Dictyosphcerium. 



** Cells in radiating series; connecting threads 



scarcely visible ; chloroplast axile Dictyocystis. 



B. Cells grouped in fours in one plane; colonies ir- 



regular Tetracoccus. 



C. Cells in botryoidal clusters. 



* Freely exposed in a thin gelatinous envelope Botryococcus. 



** Clusters covered by a firm, irregular, tough 



membrane Ineffigiata. 



Genus Dictyosphaerium Nag., 1849. The cells are globose, 

 ovoid, or subreniform in shape, with a firm cell-wall, and they are 



connected by dichotomously branched 

 threads to form a roughly spherical 

 or ellipsoidal colony. The entire 

 colony is enveloped in mucus, and 

 the cells are situated somewhat far 

 B apart towards its periphery, large 



Fig. 104. Dictyosphcerium pui- colonies often becoming very irregu- 

 chellum Wood. A, from the plank- } a r. Each cell contains a more or 

 ton of Loch Shin, Sutherland; B, , n , j . i ri i 



from Cam Fell, W. Yorks. x 450. less bell-shaped, parietal chloroplast, 



1 G. Massee in Journ. Linn. Soc. Bot. xxvii, 1891. 



