12 BRITISH MYCETOZOA. 



is found ; this is constructed before the spores are formed, and in 

 many species extends from the base of the sporangium, or from an 

 extension of the stalk within the sporangium (the columella), to the 

 enclosing wall. It often appears to form a scaffolding, which 

 prevents the shrinking inwards of the sporangium-wall in drying, 

 and thus allows the spores to mature freely and without pressure. 

 The capillitium differs widely in structure in different genera, and 

 is beautifully adapted to assist in the dispersion of the spores on 

 their reaching maturity. In Trichia the capillitium threads lie free 

 among the spores, and, being provided with spirally thickened bands 

 which are strongly hygroscopic, twist and writhe with every change 

 of moisture ; by this action they separate the spores, so that they 

 are easily carried away by the wind ; such free threads are called 

 elaters. In Stanonitis the capillitium springs from the columella, 

 and extends to the surface of the sporangium, where it forms an 

 enclosing net ; the delicate membrane covering the meshes shrivels 

 up on ripening, so that the spores lie in an open-work basket, and 

 are blown by the wind through the openings. In Arcyria the 

 capillitium consists of a dense tangle of branching threads, which, 

 when the ripe fruit dries and the delicate sporangium-wall breaks 

 up, expands to many times the original volume, and in so doing 

 scatters the spores on all sides. 



Carbonate of lime is usually abundant in the Plasmodium and 

 young sporangia of the species comprised in the subcohort Cal- 

 carinece. In most genera of the order Physaracece these granules 

 are withdrawn from the plasma before the spores are formed, and 

 are deposited partly in the sporangium-wall, and partly in vesicular 

 expansions of the capillitium. These expansions take various shapes ; 

 they are globose, fusiform, or branched, and are sometimes fused 

 together in the centre of the sporangium, forming a pseudo-columella. 

 Lime-knots. In the descriptions of the species they are termed lime-knots. In 

 the Didymiacece the granules in the young sporangia are dissolved 

 at a certain stage, and the salt forms again in crystals on the outside 

 of the wall. 



The genus Cribraria is one of several in which no capillitium 

 is present, but the upper part of the sporangium-wall consists of 

 an open net through the meshes of which the spores escape. 



It may be well to repeat what has been already stated, that in 

 the sub-class Endosporccc the formation of spores takes place several 

 hours after the sporangia have assumed their ultimate shape, and 

 is immediately preceded by the division of the nuclei by karyo- 

 kinesis, when each daughter-nucleus becomes the centre of a young 

 spore. Here, as in the case of bipartition of the swarm-cells, true 

 cell-formation takes place, and in both instances it is associated with 

 karyokinetic division of the nucleus, whereas during the growth ot 

 the Plasmodium the almost invariable rule appears to be that the 

 nuclei increase in number by simple division. 



The sub-class Exosporcce is represented by the single genus 



