2 
INTRODUCTION. 
Monograph that Van Tieghem in 1880 and Brefeld in 1884 corrected 
this view. Accepting the Mycelozoa as established by Rostafinski, 
bat excluding Dictyostelium on the ground of its not forming a 
true Plasmodium, we have a clearly defined group of organisms 
separated from all others by the following combination of 
charactei^s. A spore provided with a firm wall produces on 
germination an amceboid swarm-cell which soon acquires a 
flagellum. The swarm-cells multiply by division and subsequently 
coalesce to form a plasmodium which exhibits a rhythmic 
streaming. The plasmodium gives rise to fruits which consist 
of supporting structures and spores ; in the Endosporem these 
have the form of sporangia, each having a wall within which 
the free spores are developed. A capillitium or system of threads 
forming a scaffolding among the spores is present in most genera. 
In the Exosjm-ece the fruits consist of sporophores bearing numer- 
ous spores on their surface. 
The Spore and Swarm-cell.— The spores of the JEndosporece are 
mostly spherical, but occasionally they are ellipsoid. Their size 
is uniform in each species, or with so little variation that their 
measurement affords a valuable character for specific determination. 
This is not without exception; for instance, in the abundant 
species Leocarpus fragilis the spores are commonly 11 to 12 /a 
diameter, but in occasional gatherings they average 16 to 20 /x. 
In other genera which present ample material for comparison, 
similar variation is sometimes met with. The_ spore- wall 
is variously coloured in the different species. It is described 
by Zopf as showing the chemical reaction of cellulose, and 
consisting of a simple firm membrane ; * but the spores of several 
species of Didymium and Trichia, when crushed in an acetic 
solution of gentian-violet, show the existence of two layers, the 
inner more delicate and appearing less deeply stained than the 
outer. In Physartim, Arcyria, and genera with thin-walled 
spores, the double layer has not been traced. It is either 
smooth or marked with sculpture. The contents of the spore 
consists of faintly granular protoplasm with a single central 
nucleus. In abnormal developments, monstrous spores, often of 
irregular shape and containing several nuclei, are of frequent 
occurrence. . c 4.1 ' 
The length of time that elapses before the germination ot tfie 
spore after it has been placed in water varies with the species, 
and often in different gatherings of the same species. In the 
darker spores of Stemonitis fusca it does not begin for nine or 
twelve hours, while in the pale-spored variety it has been 
observed to occur in twenty-eight minutes. In Kehcularia 
LyG02}erdon it usually takes place in less than an hour in fresh 
gatherings ; spores from a specimen which had been stored for 
nearly three years began to germinate in four hours, and in 
twenty hours nearly every spore had done so. Didymium diffor7m 
* Schenk, "Handbuch der Botanik," Bd. iii. 2, 1884; "Die rilzthierc," 
p. 53. 
