172 THE MYXOMYCETES OF PICTOU COUNTY. MOORE 



up and becomes an amoeboid body and all fuse together to again 

 form a motile plasmodium. 



Sporangia. The structure and peculiarities of the spor- 

 angia capillitium and spores,, in so far as illustrated by our 

 known Nova Scotia forms, are more or less fully set out in the 

 detailed descriptions of the species in my collection. 



In this connection it may be stated that in the evolution of 

 the Myxomycetes, the most prominent feature is the gradual 

 perfecting of the mechanical contrivances to effectuate r^pore 

 dispersal. The most primitive form of fructification must be 

 regarded as the plasmodiocarp, consisting of a limiting mem- 

 brane enclosing a mass of spores which only escape by its 

 gradual breaking down. Such forms we find in the less special- 

 ized families of the Cribrariacece. 



Starting from this simple form there offshoot two main lines 

 of development exhibiting the gradual perfecting of two distinct 

 forms of adaptation for insuring effectual spore dispersal. 



The first consists in the modification of the sporangial wall, 

 its thickenings becoming discontinuous so that the breaking 

 down of the thinner, more delicate areas facilitates the escape 

 of the enclosed spores. This line of development is exhibited 

 through the Cribrarias to Dictydium cancellatium, where it 

 reaches its tiigest expression. In this species, the walls of the 

 ripe sporangium become reduced to a mere framework of ribs 

 connected by delicate transverse threads, the whole structure 

 dangling on the end of the stipe which is weak and tenuous at 

 its upper extremity. 



The second consists in the development of a capillitium, 

 either with or without a columella. The highest forms with 

 columella are found among the Stemonitacece in such genera as 

 Stemonitis, Comatricha and Lamproderma. The most perfect 

 adaptations for securing spore dispersal, however, are found in 

 forms destitute of a columella, such as the Arcyrias and Tri- 



