AND FACTORS WHICH INFLUENCE THEM. 143 



is similar to E but much elongated, and conventionally repre- 

 sents a few striking cases in which cylindrical forms are lengthened 

 to an extreme degree. The genera which produce them are 

 chiefly Stemonitis and Comatricha, which may almost be re- 

 garded as a single genus, the distinction between them being 

 ratherartificial, though convenient for classification. In Stemonitis 

 the sporangia are sometimes four-fifths of an inch in length 

 and fairly upright, but in Comatricha (C longa, found in Asia, 

 Africa and America) the sporangia are sometimes two inches 

 long, and are flexuose and drooping, owing to the weakness of 

 the columella. In both instances the fasciculate sporangia 

 mutually support each other during formation, but after drying 

 they are apt to separate and bend over. The only example in 

 the Calcarineae of a form at all similar is Erionema, a genus of 

 a single species. When sessile, the sporangia, which are very 

 small, frequently appear as branched plasmodiocarps ; but it 

 also presents stalked and lengthened forms, prone or pendant, 

 owing to weight of lime in the sporangium walls, and the weak- 

 ness of the capillitium which is merely an expanding network 

 of slender threads, unsupported by a columella. In all three 

 cases the form-giving effect of interior, deposits is accentuated in 

 the exceptional length of the sporangia ; but although sphericity 

 is lost, surface tension is still evident in their cylindrical round- 

 ness. Moreover, we must remember that whatever restraints 

 interior deposits may impose on the plasm while a sporangium 

 is forming, surface tension at last finds full and free expression 

 in the sphericity of the spores produced. In multitudinous 

 spore-cases of globular shape the whole of the clarified plasm 

 rests awhile till surroundings favour the renewal of its activities. 

 From this analysis we find that in the production of sporangial 

 forms, surface tension, free or restrained, is the dominant factor ; 

 that gravitation is strongly influential ; that lateral compression 

 helps to mould some of the vertical forms ; that capillary effects 

 are traceable ; and that desiccation affects more or less, and 

 sometimes much distorts, the maturing sporangia. It is un- 



