196 



Tetrasporineae 



transverse (Elakatothrix) or oblique (Arikistrodesmus falcatus var. acicularis ', 

 fig. 129 C) planes into two or four daughter-cells. Reproduction takes place 

 by the successive divisions of the protoplast to form 2, 4 or 8 spore-like 

 bodies, which in most cases assume the characters of the mother-cell before 

 being liberated. These are autospores. In the coenobic forms each mother- 

 cell gives origin to a new colony an autocolony (figs. 128 C, and 133 C and D). 

 The wall of the mother-cell is either ruptured or becomes converted into 

 mucilage, and in Oocystis may become greatly distended to form a wide 

 envelope enclosing the daughter-cells. 

 Neither zoogonidia nor gametes occur 1 . 



H 



Fig. 122. A F, Oocystis submarina Lagerh. A, vegetative cell; B, young colony; D and E, 

 Tetraedron-like cells formed within old mother-cell-wall of Oocystis; C and F, development 

 of Tetraedron-like cell to form two (C) or four (F) Oocystis cells. A and B, x 995 ; D and 

 E, x570; C and F, x 610 (after Wille). G and H, Scotiella antarctica Fritsch. G, single 

 cell viewed with the principal ridges parallel to the substratum, x 830 ; H, optical section, 

 x 430 (after Fritsch). I and J, Scotiella polyptera Fritsch. /, side view ; J, oblique end 

 view to show course of ridge?, x 1100 (after Fritsch). A' and L, two side views of Scotiella 

 nivalis (Chod.) Fritsch, x about 800 (after Chodat). 



The Alga? of this family are little removed from the most primitive forms 

 of the Chlorophyceae, and it is probable that the characteristic autospores are 

 merely arrested zoogonidia which at once develop either singly into a new 

 cell or collectively into a new coenobium. Under cultivation, and particularly 

 in cultures on solid media, some of these Alga3 are profoundly modified, but in 

 their natural state they exhibit a truly remarkable constancy of character. 

 Many of them are ubiquitous in all climates and nearly all are inhabitants 

 of fresh water. The form of the cell and the nature of the colony are so 

 varied that only a sectional treatment can give the student a clear idea of 

 the family. There are six well-marked sub-families. 



1 Consult remarks on Eremosph&ra (p. 198) and Micractinium (p. 199). 



