58 



BRITISH CHAROPHYTA. 



The surface of the membrane exhibits a 



TJi J_f _ f\f 



8 number of ridges which ascend spirally 



the oospore. ., . , , . . ,, l ~ 



from right to left, rising trom 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 convolutions 

 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 (Ghara baltica). 



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 

 ^ e p en t a ona i I 3ase already referred to 



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 



Basa c aws 



