Autosporaceas 



195 



' Chlorosphsera ' should be referred to the genus Protococcus. The Antarctic species of 

 Protococcus clearly show that there are no characters of importance by which they can be 

 separated. On the other hand, ' Chlorosph&.ra ' appears to be related to Chlorococcum 

 among the Chlorochytriese, since it produces zoogonidia (8 or more) from a single spherical 

 mother-cell. It is not improbable that the Algae described as species of ' Chlorosph&ra ' are 

 the relics of intermediate forms between Protococcus and the lowest form, viz. Chlorococcum, 

 of the Chlorochytrieee. They combine the zoogonidium-formation of the latter group with 

 the formation of transverse walls in vegetative division such as occurs in Protococcus 

 viridis and P. dissectiis. 



Family Autosporacese. 



The Autosporacese are one of the most clearly defined families in the 

 Protococcales. The Algte included in it are free-floating, solitary or colonial, 

 the cells being usually associated to form very small few-celled colonies. In 

 some cases the colony is a coenobium with a definite construction (Ccelastrese, 

 Crucigeniea?, Scenedesmus), but in most of the other forms the colonies readily 



Fig. 121. A arid B, Oocystis solitaria Wittr. C and D, 0. crassa Wittr. E and F, 

 O. panduriformis W. & G. S. West. G, O. elliptica W. West. All x 485. 



dissociate into small groups of cells or single individuals. With few ex- 

 ceptions the amount of mucus surrounding the colonies is small, but in 

 Kirchneriella and Elakatothrix there is a very copious mucous investment 

 around each colony, and in a few other forms, such as Crucigenia and An- 

 kistrudesmus Pfitzeri, there is a considerable mucous envelope. There is 

 generally one parietal chloroplast in each cell, often very large, and not 

 infrequently occupying most of the cell. It may or may not possess a 

 pyrenoid. In Eremosph&ra there are numerous parietal chloroplasts, and 

 in most species of Oocystis there are several (vide fig. 121 A, C, D and E). 

 The protoplast contains a single nucleus located in the central part of 

 the cell. 



Multiplication sometimes occurs by the division of the mother-cell along 



132 



