Mar. 3,1923 Origin of the Central and Ostiolar Cavities in Pycnidia 751 
formed in a few days. No perithecia have been seen in cultures either 
from ascospores or pycnospores. 
formation of the central cavity in the pycnidium 
The various stages are best studied in material obtained by artificial 
infection of strawberry and from cultures on agar media where the 
early stages are somewhat exaggerated and prolonged, so that the 
growth story can be followed and timed more easily than from pycnidia 
obtained on fruit and dead leaves. Sections of the pycnostroma show 
a rather homogeneous plectenchyma of thin-walled cells without any 
trace of sclerosis; consequently, as we should expect, the force due to 
the more rapid growth of the peripheral cells resulting in the rupture of 
inner cells comes most easily and naturally into play. 
When the primordium has attained considerable size, forming a 
spherical or elliptical mass of tissue 50 to 100 microns in diameter (as 
it is found on fruit or on leaves in nature it is much less), it has stored 
in it a quantity of food readily available for the developments which 
are next to take place. The sporogenous tissue will be located on a 
dome-shaped structure placed at /the bottom of the cavity similar to 
that of Coniothyrium diplodiella described by Istvanffi (7); the curve 
of the dome will correspond roughly with that of the wall above, with 
a spore cavity between the two tissues. The region in the plectenchyma 
where the cavity will first appear can be determined in advance of any 
line of rupture. There is a preliminary growth and orientation by 
which rows of vertically placed cells are laid down in a line across the 
upper central portion of the primordium. The upper cells in these 
rows stretch out or swell as gelatinization progresses, but the cells below 
the line of final separation continue to grow upward, forming a palisade- 
like row of elongated cells (PI. 4, A). As noted, the cells that first 
rupture appear to be either swollen longitudinally or stretched. If the 
rupture were due to the excess growth of cells in the periphery over that 
of the cells within, this appearance of stretching would be a natural one; 
but it should be kept in mind that there has been a vertical growth of 
the hyphae that are being ruptured. The disorganization may thus 
be due to the thrust of the growing cells into those above, or to enzym 
action. In any event these elongating cells are the homologues of 
sporophores, although the ones present at this time will not bear spores. 
The end cells disorganize and the colloidal remains stretch out as the 
cavity increases in size (PI. 5, E). The end cells slough off, new buds 
put forth, and new potential sporophores arise by division of cells of the 
enlarging dome of fertile tissue. In material grown on agar there is 
certaily a large amount of disorganization of tissue of the pycnidial 
stroma, but in nature this structure is not great, and differentiation of 
tissues begins very early so that the lysigenetic enlargement of the 
cavity is less apparent. That there is here a certain amount of cell 
destruction is evident from the cell remains still clinging to the inner 
layer of the wall of the mature pycnidium (Pis. 4, J; 6, F). So char¬ 
acteristic is this line of disorganized cells that our fungus was recognized 
in sections of oak leaves from Italy collected by Professor Massalongo 
30 years ago. 
