Ohlorangieas 



185 



In Tetraspora, if the conditions are unfavourable, during the formation 

 of zoogonidia the cells become invested in a strong resistant cell-wall and 

 become hypnospores (Gay, '91 ; Chodat, '02). 



The 'pseudocilia,' or motionless cilia, of the Tetrasporeae are unique among 

 the Protococcales. 



Sub-family CHLORANGIE^E. This is a small group of attached Algae, fixed 

 in all cases to a substratum by means of mucilaginous stalks. Physocytium, 

 which is the simplest form, is unicellular; and the stalk of attachment is 

 formed by the conversion into mucilage of the two cilia of the zoogonidium, 

 after the latter has become quiescent with the tips of the cilia resting on 

 the wall of some larger filamentous Alga (fig. HOD H), In Prasinocladus 



A 



~*4i5 



Fig. 111. Sphwrocystis Schroeteri Chodat. A and B, normal colonies from the British 

 freshwater plankton, x 450. (7. zoogonidium, x about 700 (after Chodat). 



(fig. 110 A C), Hauckia, and Chlorangium the mucilaginous stalks are much 

 thicker, and are formed by a unipolar secretion of mucilage. On the vege- 

 tative division of the cells, which is obliquely longitudinal, the mucilaginous 

 stalks fork, so that small branched colonies are gradually built up. 



In Physocytium the cells have the typical cup-shaped Chlamydomonadine chloroplast 

 with one pyrenoid, but in Prasinocladus the chloroplast is reticulated or even divided into 

 a number of parietal rod-shaped pieces, and has no pyrenoid. In Prasinocladus the 

 zoogonidia possess four cilia, but in the other genera they have only two. There is little 

 doubt that Physocytium represents one of the very first stages in the interpolation of a 

 permanent resting-state into the Chlamydomonadine life-history. Some of these Alg;e arc 

 freshwater, others brackish or marine. 



The genera are : Chlorangium Stein, 1878 ; Prasinocladus Kuckuck, 1894 [inclus. 

 Chlorodendron Senn, 1899]; Physocytium Borzi, 1883 ; Hawk!" IW/i, 1883 ; Krt>ftJI<n-y#ti'* 

 Bohlin, 1897. 



