STRUCTURE AND DEVELOPMENT. 57 



encasing and sealing them completely so that subse- 

 quent impregnation would be impossible; (c) that many 

 oogonia are found fully developed yet without this 

 coloured membrane and that these eventually become 

 disintegrated and the cell-contents scattered, for which 

 absence of fertilization would sufficiently account. 



In support of the second assumption as to the 

 origin of the coloured membrane the following 

 considerations may be adduced :- -(a) No coloured 

 membrane is found growing upwards from the base 

 of the oogonium, either at the time of fertilization or 

 at any other period, the whole oospore becoming 

 coloured simultaneously. This clearly indicates that 

 it is a membrane already encasing the oosphere which 

 becomes coloured and indurated. (b) The exterior 

 and posterior walls of the tubular spiral-cells un- 

 doubtedly separate by the breaking down of the 

 lateral walls along their line of contact, since the outer 

 portions of these cells ultimately combine to form a 

 single integument which as already stated can be 

 detached as a whole. When the contents of the 

 enveloping cells have been removed the posterior 

 walls of the enveloping cells must necessarily lie 

 underneath, but what is found here is the coloured 

 membrane of the oospore without any membrane 

 intervening. 



This membrane differs largely in different species, 

 varying in texture from thin, flimsy, or flexible, to 

 thick, tough, or semi-rigid, and in colour from pale 

 transparent yellow to deep red-brown or reddish 

 black. 



Dr. Nordstedt has examined the chemical nature of 

 the membrane and detects in it, not lignin as De Bary 

 stated, but suberin (cork) and silicic acid. 



