ON THE PILOBOLIDiE. 
151 
When the end of one of these branches arrives close to, or in 
some species passes above, the surface, it becomes swollen at 
the end into a comparatively large rounded vesicle (Fig. 1«), 
into which the dense yellow protoplasm of the mycelium 
passes and is agglomerated at the upper end. This upper 
portion of the clavate termination is then cut off from the 
mycelium by a septum (Fig. 5«), but the movement of the 
protoplasm still vigorously continues, a portion passing 
upwards through the septum, but apparently little or none 
returning. This is the function of the septum, to retain the 
protoplasm in the upper portion, in preparation for the future 
explosive phenomena. This terminal swelling will be called 
the basal reservoir , because it forms the lower portion of the 
stem; the conically dilated end of the mycelium, upon which 
the reservoir is seated, is called the mycelian apophysis 
(Fig. 14«). Both these occasionally give off quasi-rootlets 
resembling the finer branches of the mycelium (Fig. 14). 
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b. —The Stem. 
When a sufficient supply of protoplasm is accumulated in 
the basal reservoir the pressure on its walls causes some point 
thereof, either at the top, or obliquely at the side, to yield 
and grow outwards in the form of a tubular process, like the 
finger of a glove (Fig. la). This rapidly increases in length, 
remaining of the same diameter, except that it is somewhat 
acutely pointed at the apex (Fig. 2). Up this stem the 
streaming motion of the yellow protoplasm still continues; 
but there is usually visible, just beneath the summit, a clear 
colourless space, filled only with a watery fluid (Fig. 2). 
The stem continues to elongate until it attains a height, 
according to the species, of from one-fortietli of an inch to 
one inch, in one species even sometimes exceeding the latter 
height. Its final height depends upon circumstances; the 
stem of P. K/einii , which usually averages one-tenth of an 
inch or less, may, when grown in the dark, be drawn out to 
one inch or more. 
c. —Formation of the Sporange. 
When the apical growth of the stem ceases the upward 
streaming of the protoplasm still continues ; in consequence, 
in the first place the acutely pointed apex becomes rounded 
and then flattened, and finally expanded into a more or less 
spheroidal vesicle of greater diameter than the stem (Fig. 15). 
Into this the larger part of the yellow granular protoplasm 
passes, and finally a flat septum is formed at the summit of 
the still cylindrical stem, by which the contents of the 
