262 
THALLOPHYTES. 
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 ' Flov^ers of Tan ' {Mthalium 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. T.'ji.—A Plasmodium oi Didymium leucopus (after Cienkowski, X 350) ; B a fructification of Arcyria incar>tata still 
closed ; C after rupture of the wall/ and extrusion of the capillitium c p (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 diflfering 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 Chlamydomonas^ 
and indirectly also with that of Pandorina. The nucleus of these bodies subsequently 
disappears, their motion becomes more sluggish, and conjugation commences. They 
