176 THE NORTH AMERICAN SLIME-MOULDS 



the forms are indistinguishable ; the difference is a matter of 

 size, and to some extent, of the color of the wall. The speci- 

 mens are a little larger, depressed and angular. The peridium 

 is paler, smoother, though sometimes almost black, thin, rup- 

 tured irregularly. But the form and color of the peridium in 

 the sporocarps of the older species vary much in response to 

 external conditions ; on a substratum affording scant nutrition 

 the forms of fructification are minute ; and in all cases, if 

 maturity be hastened, the peridium responds in darker colors. 

 Under more favorable conditions the wall is smoother and 

 brighter. 



2. LYCOGALA FLAVO-FUSCUM (Ehr.') Rost. 



1818. DiphtJierium flavo-fnscum Ehr., Syl. Myc. Berol., p. 27. 



1829. Reticularia flavo-fusca (Ehr.) Fries, Syst. Myc., III., p. 88. 



1873. Lycogala flavo-fuscum (Ehr.) Rost., Versuch., p. 3. 



1875. Lycogala flavo-fuscum (Ehr.) Rost., Man., p. 288. 



^Ethalia solitary or sometimes two or three together, large, 

 2-4 cm. in diameter, spherical or spheroidal, purplish gray or 

 brown, smooth, shining; the peridium thick, simple, but in 

 microscopic section showing two or three successive layers ; 

 capillitium of abundantly branching, irregular, transparent 

 tubules, marked by numberless warts and transverse rings or 

 wrinkles ; spores in mass yellowish gray, by transmitted light 

 colorless, smooth or only faintly reticulate or roughened, 5-6 /u. 



This, one of the largest and most striking of the slime-moulds, 

 is by students generally mistaken for a puff-ball. It occurs on 

 stumps and rotten logs of various sorts in the Mississippi Valley, 

 more often affecting stumps of Acer saccharinum L. The 

 fructification, when solitary, about the size of a walnut, though 

 sometimes much larger; when clustered, individuals are much 

 smaller. The form depends largely upon the place in which 

 the fruit is formed. The plasmodic mass is so large that its 

 form is determined by gravity. Thus on the lower surface of a 

 log raised a little distance from the earth the aethalium is often 

 pyriform. This fact did not escape Micheli. See Nov. Plant. 



