184 



Tetrasporinew 



is central and star-shaped (Scherffel, '08 A), and the two contractile vacuoles 

 and the pigment-spot of the Chlamydomonad are retained. There is a de- 

 finite wall to each cell, but in most cases the mass of jelly is due to the 

 conversion into mucilage of its outer layers. In many instances this is so 

 complete that the jelly is structureless, but in others the cells retain to a 

 variable degree their individual envelopes (Palmodictyon ; fig. 1155). In 



the dominant vegetative state of Schizo- 

 chlamys the outer envelopes are more or 

 less persistent and the ecdysis of the wall 

 is by fragmentation (fig. 113 B). Division 

 of the cells occurs transversely or obliquely 

 in two or three directions, the daughter- 

 cells rapidly attaining their full size and 

 undergoing further divisions. In Chloran- 

 gium, Prasinocladus (fig. 110-4) and Hor- 

 mofo7a(fig.H5 C) the mucilage is secreted 

 in a unilateral manner and becomes tough, 

 branched colonies of cells on gelatinous 

 stalks being gradually built up. 



The colonies frequently become dis- 

 membered into smaller portions by the 

 disorganization of parts of the jelly, each 

 portion increasing to form a new colony. 



Asexual reproduction takes place by 

 biciliated zoogonidia of the Chlamydo- 

 monad type. They arise either by the 

 transformation of a vegetative cell into a 

 zoogonidangium in which several (4 or 8) 



x 470 ; B, a single cell showing the 

 chromatophores, x960; C, zoogoni- 

 diurn, x 900 (after Kuckuck). D H, 



Fig. 110. AC, Prasinocladus lubricns zoogonidia arise (Apiocystis ; Schizochla- 

 Kuck. A, part of a small colony, j n\ ^.i 



mys, fig. 113 C and l/), or by the as- 

 sumption by the ordinary vegetative cell 



Physocytium confervicola Borzi, x 600 of the motile Chlamydomonadine con- 

 fflftpr Borzi^. D. voung colonies at- T,- /m < mi '\ A" i 



thd to a filament of Svirom/ra- E, dition (1 etraspora). Ihe last-mentioned 



formation of zoogonidia; F, zoogoni- f ac ^ i s a valuable piece of evidence in 



favour of the view that the Palmellaceas 



dium; G, gamete; H, germination of 



have originated by the intercalation of a 



simple though well-marked vegetative condition between two formerly suc- 

 cessive motile phases. 



Gamogenesis has been observed in some of the genera by the fusion 

 of isogametes, either similar in all respects to the zoogonidia and produced 

 singly in a gametangium, or much smaller than the zoogonidia and produced 

 in numbers from a gametangium (Palmetto). 



