MYXOMYCETES. 



of them in the cavities of moist substrata, where they creep about in the form of 

 naked amoeboid masses of protoplasm (plasmodia), which according to modern 

 investigations contain numerous cell-nuclei. 



The Myxomycetes are usually first perceived when they come out of their porous 

 substrata and form their relatively large fructifications. The largest of these are the 

 flat sulphur-yellow cakes, which appear in summer on tan and are known as 'flowers of 

 tan' (Aethaltum septicum} ; the fructifications si Lycogata, which issue from the stumps of 

 trees, are of the size and shape of hazel-nuts ; in most other Myxomycetes the fructifi- 

 cations are small stalked capsules; all contain a countless number of small, roundish spores 

 with thick cell- walls. Other structures make their appearance in many cases when the 

 capsules burst; these are known as the capillitium, capillary tubes or threads often 

 combined together into a net or lattice-work, the origin of which will be explained 

 further on. In Dictyostelium mucorozdes, a species discovered by Brefeld, there is no 

 capillitium and no outer wall to the fructification, which consists simply of a stalk 

 composed of parenchymatous cells, and a small head formed of a roundish mass ot 

 spores. These spores develope on a microscopic slide in a watery decoction of rabbits' 

 dung, and produce ripe fructification in a few days. In germination the whole of the 

 protoplasm of a spore escapes from the ruptured wall, and creeps about with amoeboid 

 movement, and feeds and grows. In 

 other Myxomycetes (Fig. 8) a swarm-cell 

 passes out from the spore provided with 

 a cilium, a nucleus and a contractile va- 

 cuole, and dances and hops about by 

 vigorous motion of its cilium accom- 

 panied by change of shape, and has also 

 a creeping movement over the substra- 

 tum on which it lies and puts out pro- 

 cesses on every side. Eventually the 

 cilium is drawn in, and the cell passes 

 definitively into the amoeboid condition 

 (Fig. 8), which the product of germina- 

 tion in Dictyostelium assumes from the 

 first. After a few days, when the amoe- 

 boid bodies have increased considerably 

 in size, they multiply by repeated divi- 

 sion. Later on their movement grows 



more sluggish, the amoeboid bodies collect in groups, cling closely to one another, and 

 finally unite together to form larger masses ; when one such mass is formed the rest 

 creep towards it from all sides as to a centre and unite with it, and thus increase the 

 size of the protoplasmic body, which eventually rounds itself off more and more. 

 Though some of the details of^this proceeding require further observation, yet it can 

 scarcely be disputed that we have here not a real coalescence of the constituents of the 

 protoplasmic body 1 , of nucleus with nucleus, protoplasm with protoplasm, as in a 

 sexual act in the Conjugatae or Mucorineae, but only a more superficial union of 

 masses of naked protoplasm. A similar proceeding may be observed in other cases, as 

 in the mycelia of many Basidiomycetes, where the cells come into close union with one 

 another over considerable areas without suggesting the idea of a sexual act. The 

 arranging of the motile cells of Hydrodictyon into a net (p. 40) may.be quoted as an 

 analogous proceeding, and it is to be observed that there too the amoeboid bodies have 

 no cell-wall. The plasmodium of Dictyostelium continues but a short time in the 



FIG. 8. Physarum album, i spore ; 2 contents issuing from a 

 spore ; 3 the contents when set at liberty ; 4, 5 the same as a swarm- 

 cell with one cilium ; 6, 7 after loss of the cilium ; 8, 9, 10, n coales- 

 cence of amoeboid bodies ; 12 a small plasmodium. After Cienkowski. 



1 In Guttulina rosea, a very simple Myxomycete, the amoeboid bodies according to Cienkowski 

 (Bot. Jahresber. 1873, p. 61) are only heaped together, and do not coalesce. 



