EUPHYCOPHYTA 



53 



Microspora with its cell walls in two pieces has an analogue 

 with Tribonema in the Xanthophyceae and it seems that this type 

 of construction has arisen more than once in the course of 

 evolution. 



Cylindrocapsaceae : Cylindrocapsa (cylindro, cylinder; capsa, 

 box). Fig. 25 



The single genus of the family is fresh-water and each plant 

 consists of unbranched filaments attached at the base by means of a 

 gelatinous holdfast. When young each thread is composed of a 

 single row of eUiptical cells with thick, stratified walls, the whole 

 being enclosed in a tubular sheath. Each cell contains a stellate 



Fig. 25 Cylindrocapsa. A, vegetative filament. B, thread with young 

 antheridia (n) and young oogonium (0). C, fusion of gametes. 

 a = antherozoid, o =ovum. D, old mature filament. (After Fritsch.) 



chloroplast and a single pyrenoid. In older filaments the cells divide 

 longitudinally, usually in pairs, and this suggests how genera such 

 as Monostroma may have evolved. Reproduction in this genus is 

 more advanced than in allied genera because, apart from bi- or 

 quadriflagellate zoospores, sexual reproduction is oogamous, the 

 plants being monoecious or dioecious. Each antheridium gives rise 

 to two biflagellate antherozoids and each oogonium to a single 

 ovum. 



