A Afonorjnrph of the Myjroga^tres. 33 



thickened, and at the period of maturity, the thickened portions 

 are persistent, while the remaining portions of the wall dis- 

 appear, and as this thickening is usually of a determinate 

 nature, and utilized as a generic factor, we meet with the small, 

 fairly regular openings in the lateral walls presented by one of 

 the members of the genus Entcridium, or the still larger 

 openings of Clathroptychium ; but, although the modification is a 

 step in the right direction, owing to the fact that the species 

 constituting the two genera named retain the aethalioid con- 

 dition, the new idea is of but little practical value; and it is only 

 when we come to Crihortria, the components of Avliich for the 

 most part have reached the condition of forming small detached 

 Plasmodia, each only sufficiently large to form a single spor- 

 angium, that we realize the value of the perforated sporangial 

 wall, which, other things being equal, is better than the sealed 

 up, entire sporangium, inasmuch as at the moment the spores 

 are mature, there is a chance of being removed from the 

 sporangium by wind or rain ; but in Crihraria the stem, although 

 usually elongated, is rigid, and it is in the genus Didydium that 

 arrangements for spore diffusion from a perforated sporangium 

 is most perfect. In this genus the thickened, permanent 

 portions of the sporangium are arranged in the form of ribs 

 radiating from the base and converging again at the apex, being 

 connected by very thin, transverse bars, forming a hollow sphere 

 of lattice-work ; this globe is pendulous from a long stem curved 

 at the apex, and while the stem is rigid during the young 

 'condition, towards maturity the upper portion above the curve 

 becomes shrivelled and flaccid, and the sporangium hangs in 

 a condition ready to be dangled by the wind or the movements 

 of minute insects ; how effectual this method of spore diffusion 

 is in its way is proved by the specimens being generally found 

 destitute of spores. In Entcridium, as already mentioned, we 

 find in one species the wall symmetrically perforated, whereas 

 another species has the walls of the component sporangia 

 forming the aethalium so irregularly perforated, and forming a 

 variable network, that at first sight the aethalioid nature of the 

 mass is masked, and this species may be considered as forming 



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