158 Weston.—The Development of 
Sporangia. Typical sporangia of Thraustotheca are broadly clavate in 
shape, and lack papillae of dehiscence. Variations from the type to a 
fusiform or subspherical shape may occur; and in size the sporangia may 
show all gradations, from the largest, about 300 by 60 fx, containing several 
hundred, to small impoverished specimens containing only a few spores. 
Renewal of the sporangia takes place not only by cymose branching, the 
only method heretofore noted, but also by successive formation in basipetal 
series (Fig. 27 ). 
Formation of sporangia by the mycelium follows a diminution of the 
food supply in accordance with the general law established by Klebs (18). 
Since certain important details in the process of sporangium formation could 
not be made clear by serial sections, a study of the living material was 
made. The following description is derived from observations on a large 
number of sporangia in hanging-drop cultures under a Zeiss J. water- 
immersion lens. 
The process begins with a gradual accumulation of protoplasm and 
a proportionate enlargement of the hypha, generally at the tip (Fig. 1 ). 
Eventually the accumulating content fills the sporangium initial, leaving at 
most only a small axial vacuole (Fig. 2 ). A septum is now formed 
across the sporangium base. The granular protoplasm in this region 
suddenly separates, leaving a hyaline zone (Fig. 3 ). At the bottom of 
this zone the septum is formed (Fig. 4 ), while at the periphery the 
lateral sporangium wall is reinforced, and in a few moments the granular 
content moves back, obliterating the hyaline area. Because of its reinforce¬ 
ment (cf. Fig. 29 ) the basal part of the sporangium wall is especially 
persistent, a peculiarity of the genus noted but not explained by previous 
investigators. Occasionally the septum shows columella-like outgrowths 
into the sporangium (Fig. 36 ); but as a rule the statement of Solms- 
Laubach and others that the septum is strongly bulged out into the 
sporangium is not confirmed. 
The content now undergoes differentiation into a number of spores. 
The first step in this process is the separation of the protoplasm into 
spore initials. Irregular clefts filled with cell-sap (Fig. 6 ) appear in the 
centre of the sporangium, and extend (Fig. 7 ) to form a system of 
intersecting lacunae (Fig. 8 ) which divide up the sporangium contents 
into roughly polygonal spore initials. Since the sporangium content, in 
spite of this division, contracts as a whole when plasmolysed, we may infer 
that a thin peripheral layer of protoplasm still remains fincleft. 
A rapid change in the appearance of the sporangium now indicates that 
a second phase in its development has begun. The content suddenly 
becomes translucent and temporarily vacuolate, while the individual spore 
initials become less distinct than heretofore (Fig. 9 ). This is probably the 
result of a loss of cell-sap with a consequent shrinkage of the sporangium 
