46 THE MYXOMYCETES 



cies of true slime molds. As their name implies, they were first 

 placed among the Gastromycetes and, in fact, were so retained 

 by Fries. Their most common habitat is rotten logs or wood 

 and decaying leaves. Many possess unusual architectural beauty 

 and vividly striking colors. The majority of known species 

 grow in temperate regions and are quite cosmopolitan. Some, 

 however, appear to be restricted to the tropics. 



The shme molds are characterized by having, in their assimila- 

 tory phase, naked, amoeboid, multinucleate plasmodia that are 

 quite mobile and that vary in size from microscopic units to 

 masses several centimeters in diameter. These plasmodia are 

 hyaline and white, yellow, orange, red, violet, blue, green, or 

 brown. The colors are imparted by anthracene pigments, and 

 a change in reaction results in a change of color. The plasmodia 

 occur largely within or beneath decaying vegetation, but at the 

 time of reproduction they migrate to the exposed surface of the 

 substrate or creep up on near-by green herbs or the bases of 

 trees. The migration of the plasmodium never fails to charm the 

 observer. In his Sy sterna Mycologicwn Fries writes, "At one 

 time I deposited the plasmodium of Diachaea in my hat and 

 within the space of an hour it had covered the greater part of it 

 w'lxh its elegant white network. ... I find nothing more won- 

 derful than slime molds in all the world of plants." 



The fructifications are of several general types, all possessing 

 an outer membranous covering of inert material, the peridium. 

 If the entire plasmodium becomes transformed, as in Fiiligo sep- 

 tica, into a fructification without the delimitation of separate 

 sporangia, the reproductive structure is of the type termed an 

 aethalium. If the plasmodium aggregates at the loci of a few of 

 the larger veins and retains somewhat the netted form of the plas- 

 modium, as in Hemitrichia serpiila, the fructification is termed a 

 plasmodiocarp. If the plasmodium becomes separated into 

 grouped, erect clusters of fructifications of definite form, with 

 remnants of inert material remaining at the base, the fructifica- 

 tions are termed sporangia. Sporangia are of many patterns, 

 some being marvels of delicacy and intricacy. 



Fruiting may be induced by exhaustion of nutriment [Camp 

 (1937)]. Doubtless other environmental influences stimulate 

 transformation of the plasmodia into fructifications. 



