119 
pycnidia, made their appearance upon the stroma. They are usually 
arranged more or less in circles. In old stromata one often sees several 
concentric circles of pycnidia, since uew rows are constantly being 
formed toward the circumference. 
The pycnidia appear first as small knots of hyphse ; in certain places 
in the stroma the hyphae wind much closer together; these points there¬ 
fore appear darker, and are easily seen. These knots steadily increase 
in circumference for some time without any kind of differentiation. They 
represent merely small outgrowths of the stroma, nor do sections 
through this immature stage show anything but a homogeneous mass of 
hyphae. Next, the young pycnidia begin to turn brown, that is, the outer 
layer of the tissue becomes dark colored and can be clearly distinguished 
as the rind. The remaining portion of the pycnidium remains un¬ 
changed until finally the hyphae in the center move apart from each 
other, forming a small cavity (Fig. 10). This arises from the cessation 
of growth within the tissue, while the body continues to grow at the 
periphery. In this way the pycnidium develops into a spherical body 
containing a large cavity. Below, it is a little immersed in the stroma, 
but is distinctly separate/:! from it by the outer layer. The wall is com¬ 
posed of two layers, the rind and a clearer layer within, also composed 
of irregularly interwoven hyphae, without a trace of pseudo-parenchy- 
matic structure. Immediately after the cavity begins to form, hyphal 
branches grow out into it and form a continuous hymenium. They 
cut off very small, cylindrical spores in great numbers. When the pyc¬ 
nidium is mature it ruptures in an irregular manner at the point, and 
the spores emerge in waxy, yellow, or whitish, worm-shaped masses. 
In the preceding description a single pycnidium developing without 
any hindrance has been considered, but it is often the case that the first 
stages of any pycnidia arise close together. On account of the enlarge¬ 
ment of the knots of hyphae they collide, assume irregular forms, and 
grow together into various shaped bodies, yet in such a manner that the 
bounding lines of the individual pycnidia can be seen by the depressions 
between them. A rind following the depressions is formed on the out¬ 
side; but within, the lateral walls are broken through by the formation 
of the cavities so that the compound body made up of many pycnidia 
possesses but oue cavity. The depressions mentioned above correspond to 
projections upon the inside. The w T alls, consequently, appear wrinkled. 
Now, are these pycnidia homologous with those with which the inves¬ 
tigation started, the Gytispora f In the first place it may be stated that 
the form of the basidia and spores is the same in both, although they 
are as a rule a littl e smaller in the cultivated pycnidia. The structure of 
the walls agrees in the two, at least when the Gytispora pycnidia are 
young. The same things many be said of the older, black, and thick- 
walled pycnidia that have been said above concerning the stroma. The 
difference is more marked,because in the artificially produced specimens 
the pycnidia are superficial, while in the natural ones they are sunken 
