408 



Heterococcales 



only species is Chlorothecium Pirottse Borzi and should it be shown that the cells of this 

 Alga are able to give rise directly to zoogonidia then the genera Ckaraciopsis and 

 Chlorothecium would have to be united. As it is, the distinction between them is very 

 slender. Borzi figures the zoogonidia with one cilium, as he also does in Mischococcus, but 

 it is probable that the shorter cilium was overlooked. 



Ckaraciopsis gi'eatly resembles the genus Characium in the Protococcales and the two 

 genera have not only been greatly confused in the past, but they are by no means properly 

 understood at the present time. (Compare Lernmermann, '14, and Prints, '14.) 



Family Chlorobotrydaceae. 



This family includes a number of free-floating unicellular Algoe with firm 

 cell-walls. In Botrydiopsis, Pseudotetraedron and Centritractus the cells are 

 solitary, in Cldorobotrys they occur in fairly regular groups of 2, 4 or 8 

 enveloped in mucilage, and in Polychloris they are so aggregated that they 

 are sometimes angular by compression. The firmness of the cell-wall is 

 undoubtedly a character of the family and, in Cldorobotrys, Bohlin ('01 B) 

 states that the wall contains silica although it is not brittle. The amount of 

 silica must, however, be very small ; less, even, than in some Desmids 1 . 



In Pseudotetraedron (vide Pascher, '13 A) and in Centritractus the cell-wall 

 consists of two halves, one of which slightly overlaps the other. It would 



also appear from Bohlin's account 

 of specimens from the Azores that 

 the wall of the cylindrical cysts of 

 Chlorobotrys regularis consists of two 

 halves, but in the vegetative cells of 

 Cldorobotrys the wall is continuous. 

 The cells are globose except in 

 Pseudotetraedron and Centritractus ; 

 in the first-named genus they are 

 rectangular when seen from the front 

 and compressed when seen from the 

 side or end. In this genus the cells 

 are also furnished with four long 

 bristles, one at each angle of the 



Fig. 259. Botrijdiopsis arri, iza Borzi A, vege- f ront v i ew< J n Centritractus the 

 tative cell; B, formation 01 aplanospores ; 



C, formation of zoogonidia. All x 600 (after cells are cylindrical with somewhat 

 Borz,, from Wille). swollen conical extremities, each of 



which is furnished with a long bristle. There are two to many parietal 



1 Chlorobotrys is very abundant in the bogs of the British Islands (from which situations it 

 was first described as Chlorococcum regulare W. West) and the present author has found that 

 boiling in fuming nitric acid dissolves the walls more easily than in some species of Pleiirotteniiim 

 and Etiastrum. 



