132 
R. A. HARPER 
out the essential features of the cleavage process free from all possible 
bias as to the distribution of the nuclei, the angles which the cleavage 
furrows make with each other, the outlines of the whole mass and the 
general progress of the process from the periphery to the interior of the 
spore-plasm. The material was collected near Madison, Wis., fixed 
in Flemming's weaker solution and stained in most cases with the 
triple stain though certain of the photographs are from iron haema- 
toxylin preparations. 
At a stage when the sporange has reached its full size (fig. i) 
and is still milk-white in color the spore-plasm is dense and finely 
granular in the peripheral region and in the region immediately ad- 
jacent to the columella. The middle zone of the sporange on the other 
hand is still very vacuolar and almost foamy. This represents a 
condition in which the condensation of the protoplasm in preparation 
for the formation of spores is complete, except in the interior of the 
mass. The persistence at this stage of numerous vacuoles in this 
central region perhaps indicates that a gradual reduction of the cell 
sap has already been taking place during the early development of 
the sporange. If the sap passes off by evaporation the vacuoles will 
persist longer in the central region of the protoplasm. 
The capillitium is already formed before the condensation of the 
protoplasm has been completely accomplished (fig. 2). It consists in 
Didymium of fine, smooth threads which pass radially outward from 
the central, dome-shaped columellar cavity to the peridium. The 
capillitial threads are attached at each of their ends, and we have 
thus in some respects a condition similar to that in Stemonitis where 
the capillitium consists of threads branching from a central stalk-like 
columella and ending peripherally in a very delicate network beneath 
the peridium. In Stemonitis the radial branches of the capillitium 
subdivide very freely; in Didymium, on the other hand, the capillitial 
strands branch scarcely at all. When they do divide the branches 
form a very acute angle with each other and run on almost parallel 
toward the periphery. As a result it is not difficult to find in sections 
lying in the proper plane some fibers that run from the center to the 
periphery in the plane of the thin microtome section. When mature 
the capillitial threads are smooth and polished and dark colored. In 
these early stages the protoplasm is in most intimate contact with the 
surface of the capillitial threads throughout (figs, i and 2). There 
is no tendency to the formation of vacuoles about the threads nor for 
