56 



BRITISH CHAROPHYTA. 



enveloping cells are not distinguishable beneath, 

 having been utilized, as it would seem, to form the 

 membrane of the ripened oospore as explained below, 

 When the exterior integument and the 

 contents of the spiral-cells have been 

 removed they reveal the oospore — a minute hard 

 nut-like body, ranging in colour from light yellow, 

 through varying shades of red and brown, to black, 

 varying in shape from spherical to narrow-ellipsoid, 

 differing also largely in size, consistency, and opacity. 

 The oospore is found to consist of a series of 

 delicate membranes, some coloured, some colourless, 

 enclosing and protecting the spore-contents. These 

 membranes are an important factor in the discrimina- 

 tion of the various species and therefore call for 

 careful and detailed description. They may be classed 

 as follows : — 



1. The outer coloured membrane. 



2. The inner coloured membrane. 



3. The outer colourless membrane. 



4. The inner colourless membrane. 



The fully ripe and developed oospore 

 1^ ^^j possesses a tough coloured outer mem- 

 membrane ^^^^^® which closely envelops and seals 

 the inner contents. The oi"igin of this 

 membrane is not certain, but there seems to be good 

 ground for believing (i) that it follows as a result 

 of the fertilization of the oosphere, and (ii) that it is 

 formed from the posterior walls of the enveloping 

 cells. 



In support of the first assumptign we have the 

 following facts : — (a) That this membrane does not 

 develop till the oogonium is fully matured; (b) that 

 it forms a tough coating round the spore-contents. 



