8 THE LOWER FUNGI— PHYCOMYCETES 



ate and its nuclei increase in number by mitosis as it feeds and 

 enlarges. As it passes over or through the substratum it ingests 

 particles of bark, bits of dead leaves, and other debris often in 

 sufficient amount to cause a change in its color. These are 

 taken in, the available food assimilated, and the refuse material 

 usually ejected in the wake of the moving Plasmodium. Practi- 

 cally all the species live a purely saprophytic existence, but some 

 are capable of enveloping and dissolving living materials such as 

 the fruit bodies of higher fungi. The growing plasmodium has 

 a consistency similar to that of egg albumen. In color it ranges 

 from pearly white through shades of cream, yellow, and orange, 

 to red, brown, or violet. The color is to a degree definite in a 

 given species, but it changes from day to day due to metabolic 

 processes and is dependent somewhat on the amount of unassim- 

 ilated materials present in the cytoplasm. When the Plas- 

 modium Hes on the surface of the substratum it may form a thin 

 film of irregular outline, but when permeating the crevices of a 

 decaying log it becomes a much branched network of strands. 



After an extended period of vegetative activity the plasmodium 

 flows out upon an exposed surface, and contracts into a cushion- 

 shaped mass. It is then ready for transformation into the 

 fruiting phase. The Myxomycetes are split into two primary sub- 

 divisions on the basis of the character of the fructification which 

 is then formed. In the Exosporeae, including only the genus 

 Ceratiormjxa, the fruiting structure is columnar and bears spores 

 over its outer surface, each at the end of a minute sterigma. 

 In the Myxogastres the spores are borne inside the fructification. 

 It is usually then called the sporangium. If the sporangium is 

 irregular or sinuous in form it is termed a plasmodiocarp. If 

 several imperfectly delimited sporangia become partially fused 

 and develop into a compound fructification it is called an 

 aethalium. It will be sufficient here to describe the development 

 of the typical sporangium. 



Over the surface of the cushion-shaped plasmodium the 

 protoplasm is pushed up at numerous points to form definite 

 papillae. These soon elongate into tiny columns, each of which 

 develops into a sporangium. The base of each column contracts, 

 and, in species having stipitatc sporangia, forms a slender tubular 

 stalk through which the protoplasm passes upward into an 

 enlarging inflated terminal vesicle that later contains the spores. 

 As the protoplasm advances refuse material is thrown out, and 



