Some Questions which they Suggest. 43 



sporangia. If one of these forms be better than the other, 

 why does it not universally prevail ? and why do some 

 individuals of some species halt between the two opinions ? 

 We certainly do not know. This is one of the many cases 

 in which it is at least very difficult to see any advantage 

 gained by the variations of development of an organism. 



SPORANGIUM WALLS. The walls of the sporangium vary 

 very greatly ; sometimes they consist of a single membrane ; 

 sometimes of two or even three membranes ; sometimes 

 they continue till by rupture they let loose the spores ; in 

 other cases, the whole, or the upper part only, early falls 

 away and discloses the system of hairs and the spores 

 within; sometimes, as we shall see, they are furnished 

 with lime, at other times they are without it. 



In Cribraria (Fig. 5) we have a very beautiful form of 

 sporangium, the wall of the lower half persists and forms 

 a cup, whilst the upper half in its mature state consists of 

 a network only of slender threads more or less thickened 

 at the points where they cross one another. 



In Dictydium we have again another very beautiful form 

 of sporangium it consists of rays of longitude gathered 

 together at the pedicel and at the top as their two poles, 

 with much slighter transverse lines of latitude. The inter- 

 vening membrane falls away in whole or in part, and 

 leaves for the sporangium a basket of most delicate net- 

 work (see Fig. 11). 



In some cases the exterior of the sporangium has a most 

 delicate surface, shining with iridescent colours. The 

 Lamproderma is a genus with several species distinguished 



