212 Chlorophycece 



zoogonidia which swarm in a vesicle as in Pediastrum. On 

 becoming quiescent they arrange themselves in pairs and assume 

 the form of the adult cells, each pair forming one coenobium. 



E. Richteri (Schmidle) Lagerh. is only known in the British Islands from 

 Cornwall. Length of coenobium 10 40 p., breadth 6 25 p, (fig. 86). 



Family 7. PROTOCOCCACEJE (or AUTOSPORACE^3). 



The Alga? included' in this family are free-floating, solitary 

 or colonial, and are most commonly associated to form minute 

 colonies of a definite construction. The cells are sometimes firmly 

 united to form a definite coenobium, as in Coelastrum and Sorasirum, 

 but as a rule the colonies easily dissociate into single cells or 

 smaller groups (or families) of cells. With few exceptions there is 

 very little mucus surrounding the colony. There is generally one 

 chloroplast (sometimes many) in each cell, parietal or occupying 

 the whole cell, and with or without a pyrenoid. There is one 

 cell-nucleus. 



Multiplication takes place by the successive division of the 

 cell-contents either to form spore-like bodies which assume the 

 characters of the mother-cell before being liberated, or to form 

 colonies which on liberation resemble the mother-colony in all 

 except size. These are known respectively as autospores and 

 autocolonies. Multiplication by autospores, although such a 

 characteristic feature of the Protococcacea?, is not confined to this 

 family, as it occurs in Pediastrum, Radiococcus and certain other 

 genera. 



Reproduction by zoogonidia or gametes is unknown except in 

 the genus Dictyosphasrium. 



The Alga? of this family are well marked off from the Pleuro- 

 coccacea? and Palmellacese by their definite colonies and by their 

 method of multiplication. They are little removed from the most 

 primitive forms of green Alga? and a few of them are capable of 

 profound modification by cultivation in different media. In their 

 natural state, however, they exhibit a remarkable constancy of 

 character and many of them are ubiquitous in all climates. 



The family is best subdivided into the seven following groups : 



Sub-family I. Codnstrcce. Cells primarily globose or broadly 



lunate, forming a definite spherical or polyhedral coenobium. 



Sub-family II. Crucigeniew. Cells of variable form, arranged in a 



regular flat plate. 



