262 



THALLOPHVTES. 



The Myxomycetes generally first make themselves visible at the time when they 

 emerge from their porous substratum, and form their comparatively large fructification. 

 The largest of these are the sulphur-yellow bodies which appear in summer on tan- 

 heaps, and which are known under the name of ' Flowers of Tan ' {jEthalium septicum) ; 

 those of Lycogala, which are found on the stumps of trees, are of the size and form of 

 hazel-nuts. In most other Myxomycetes the fructification is a small stalked capsule, 

 containing, like those already mentioned, an enormous number of minute roundish, 

 thick-walled spores. "When these capsules burst, other structures often make their 

 appearance, to which the term Capillitium has been given : — capillary tubes or threads, 

 often united together in a reticulate or lattice-like manner, to the origin of which we 

 shall recur presently (Fig. 172, C). In the simplest form at present known, Dictyostelium 

 mucoroides discovered by Brefeld, not only is the capillitium wanting, but also the outer 

 wall of the fructification, which consists only of a stalk composed of parenchymatous 



FIG. \T2.—A Plasmodium of Dtdymium leucopus (after Cienkowski, x 350) ; B a fructification of Arcyria incarnaia still 

 closed; C after rupture of the wall/ and extrusion of the capillitium cp (after De Bary, x 20). 



cells and of a roundish mass of spores. It is instructive to dwell on this simplest form 

 of the Myxomycetes in order to arrive at an understanding of their systematic 

 position. The spores of Dictyostelium will develope on the stage of the microscope 

 in an aqueous decoction of rabbit's dung, and produce ripe fructifications after some 

 days beneath the eye of the observer. When the spores germinate, the entire pro- 

 toplasm of each of them escapes from the ruptured wall, creeps about with an 

 amoeboid motion, absorbs nutriment, and grows. It cannot be doubted that these 

 amoeboid bodies must be regarded as zoogonidia, only differing from ordinary ones 

 in their mode of motion. After they have increased considerably in size in the course 

 of several days, they divide, and multiply repeatedly in this way, a process which may 

 unquestionably be compared directly with the vegetative propagation of Cklamydomonasy 

 and indirectly also with that of Pandorina. The nucleus of these bodies subsequently 

 disappears, their motion becomes more sluggish, and conjugation commences. They 



