Helminthostachys zeylanica. 181 
the young tetrads more and more completely from one another (Fig. 18). 
At first these plasmodial strands consist solely of cytoplasm, unaccompanied 
by nuclei, which remain in the peripheral envelope. Soon, however, we 
can observe the nuclei dipping into the broader arms of cytoplasm and 
making their way into the interior of the sporangial cavity. As the round 
or oval nucleus passes into the strand of cytoplasm it usually alters its 
shape and becomes drawn-out, often into a very fine point, at its anterior 
extremity (Fig. 7). It usually stains more deeply at this beak-like process 
than it does at its blunt, posterior end. As it moves further along the 
strand and passes between the spore-tetrads it not infrequently assumes 
an elongated form, sometimes almost justifying the term vermiform, until 
it temporarily comes to rest at this or that spot, when it reassumes a more 
iso-diametric shape. The tapetal plasma, which has a finely vacuolated 
structure in successful preparations, contains an abundant supply of starch. 
All the cells composing the walls of the sporangium are rich in starch ; the 
membranes of these cells give the pectic and cellulose reactions. The 
spores remain associated together in groups of four throughout the greater 
part of their development. They now rapidly increase in size, but their 
walls remain very thin and the cytoplasm they enclose is scanty. In con- 
sequence of this the spores, at this stage, are nearly all collapsed in the 
alcohol material (Fig. 19). The young spores are tetrahedral in shape and 
the edges of those surfaces which adjoin one another in the neighbouring 
spores of a tetrad are raised up into ridges. In this way each spore 
develops three ridges upon its surface, and these ridges converge to a 
common point (Fig. 8,#). 
Early in the history of the spore one can see that the sides of the 
tetrahedron which meet at the ridges are only very loosely joined together. 
The action of various reagents, and even the pressure of the microtome 
knife, often leaves the spore with three flaps entirely separated from one 
another at the ridges, as is shown in Fig. 8, b. The cuticularized wall of the 
spore now grows somewhat in thickness, and at about this time a new 
layer — the endospore — makes its appearance within it. This layer, which 
gives the reactions of a pectic body, can be traced as a continuous, 
although delicate, layer over the entire inner surface of the spore-wall. 
In microtome sections which have passed through the apex 1 of the 
spore we can trace a little process or fold of the endospore which has 
pushed between the ridges of the exospore and which reaches to the outer 
surface (Fig. 9). In spores measuring about 23 /x across their longest 
diameter the exospore has become sufficiently thick to prevent the collapse 
of the spore in alcohol. The surface of the spore is still smooth and its 
protoplast poor in substance 2 . 
1 Viz., the point at which the three ridges meet. 
2 It usually contains a very little starch, however. 
