Mar. 3,1923 
Origin of the Central and Ostiolar Cavities in Pycnidia 757 
aecidia of the rusts [Peridermium, Adams (ji)], where the gametes are 
intercalary cells below in a series of sister cells which are becoming dis¬ 
organized or have been sacrificed in order to make space and to furnish 
food for spore production. In Schizoparme straminea the cavity is 
largely schizogenetic, although in artificial cultures on agar there is a 
large amount of cell destruction. 
Some information has been obtained showing that the same factors, 
disorganization and inequalities in growth, are operative in ostiole forma¬ 
tion. In view of the fact that the natural relative positions of the 
sporogenous tissue and the ostiole can be altered in a very striking manner 
in cultures of Schizoparme straminea it is much less difficult to conceive 
of a localized weakness in the pycnostroma determined by metabolic 
changes leading to disorganization which initiates cavity formation than 
it is to understand how the two different regions of rupture initiating 
the central cavity and the ostiole can be provided for so long in advance 
in a purely mechanical way. 
In Phyllostictina carpogena there is usually a secondary cavity formed 
in the necklike extension of the immature pycnidium. This is an ellip¬ 
tical cavity which is finally continued downward into the pycnidium 
and thus becomes a part of the ostiole. Not infrequently it becomes 
from the first a superficial accessory pycnidial cavity lined with sporo- 
phores which cut off spores. These sporophores soon become gelatinized 
and an opening is formed connecting the two cavities. Sometimes the 
ostiolar portion is rather small and the cavity is lined with short periph- 
yses, showing in a very striking manner that sporophores and periphyses 
of this species are homologous structures, or that periphyses may on 
occasion cut off spores. 
The picture of Schizoparme straminea (PI. 4, E) shows that no sooner 
has an opening been effected in the pycnidial wall by means of disor¬ 
ganization than the cells about the opening bud out or proliferate rapidly, 
growing into the space and turning upward, after which some of the 
cells at the ends of these new hyphse in their turn become disorganized. 
What is it that stimulates the comparatively old wall cells to such a 
rapid renewal of growth? We see that there must be a change in pres¬ 
sure, and a new supply of food readily assimilable is furnished by the 
destruction of cells next to them. Even the swollen cells of the buffer 
tissue seemingly almost devoid of cytoplasm are still able to grow once 
the adjacent cells furnish a little food through disorganization. 
SUMMARY 
The intermediate stages in the development of the pycnidia of three 
species of fungi associated with fruit rots have been studied, and in each 
case it has been shown that the initial stage in cavity formation consists 
in the disorganization of cells in a certain region, accompanied by a 
swelling of the cell remains. The pressure thus resulting tends to enlarge 
the cavity, maintain a symmetrical contour, and contribute further 
toward cell destruction or change of form. Further enlargement of the 
cavity may be effected by the growth of elements already present or by 
the addition of new tissue. 
In Phyllostictina carpogena the cavity is formed lysigenetically for the 
most part, although occasionally excessive peripheral growth plays 
some part in the process, especially if cavity formation begins early or 
before sclerosis has become far advanced. 
