58 BRITISH CHAEOPHYTA. 



The surface of the membrane exhibits a 



., S s o nmuber of ridsfes which ascend spirally 

 the oospore. „ . , ° „ . . „ ^ n 



from right to left, rising ii"oxq the nve 



angles of a minute pentagonal base (Fig. 25 ii), and 



meeting at the apex in a series of curved lines forming 



an eccentric pattern (Fig. 25 i). These ridges, both 



in their form and in the number of convolu.tions 



visible, are more or less constant for each species 



and serve as an aid to determination. The ridges 



sometimes exhibit little more than a thin line, more 



often they are strongly developed, and not infrequently 



they extend into a prominent wing or flange. The 



Fig. 25.^ — Terminal disposition of ridges of oospore, i. View of apex 

 {Nitella capillaris). ii. View of base (Cfeara 6oMica). 



ridges owe their origin to the overlying enveloping 

 cells, the sutures on the posterior side of which become 

 filled up as the membrane develops and hardens. 

 The number visible varies according as the spiral-cells 

 complete one, two, or three convolutions. 



In some species of Ghara the angles of 

 asa c aws ^-^^ pentagonal base already referred to 



EUlu. CF6SL i- cj e/ . 



are prolonged downwards into claw-like 

 processes which attain sometimes considerable length 

 and often form a double stage by a transverse growth, 

 giving the appearance of a little cage enclosing the 

 stalk-cell. The Nitellse do not produce basal claws, 

 but conversely in some species the flanges of the 



