180 
MorRPSOLOGY. 
Perithecia have been found on cankered areas of the twigs of the Avocado pear (Persea 
Americzna). Thev are usually scattered, standing separate from one another. Sometimes, 
however, thev occur in small groups of two to four, and occasionally thev have been found 
so closely crowded as to form a pseudo-stroma, bat no true stroma has been observed. 
They are buried in the cortical tissues, but at maturity the papillate ostiole breaks through 
to the surface and protrudes slightly. 
The form of a typical perithecium is shown in fig. J, which is a camera-lucida drawing 
from a medial longitudinal section. The form is subglohose or broadly ellipsoid, 130-190 u. 
in the horizontal diameter and 100-120 in the vertical diameter. The average dimensions 
are about 170 4 & 100 mm. 
Fig. 1. 
Section through a perithecium of Physalospora perseac. 
The wall is differentiated into two layers: the thickness of the outer layer is variable 
being thinner or almost absent at the base, and thickest at the sides near the base, where 
it is 16-24 nu thick. The pseudo-cells are brown, polygonal, 4-5 » in diameter, or somewhat 
flattened. Within this there is an inner layer of delicate, colourless, compressed hyphae 
of much more uniform thickness. 
The papilla is usually central, bat may be oblique : it is 80-100 u long and 30-50 u in 
diameter, and its walls show two distinct layers similar to those observed in the sides of the 
perithecium ; the ostiole appears in section as a narrow passage between the walls of the 
papilla. The asci interspersed with paraphyses fill the cavity of the perithecium, and 
there are numerous thread-like periphyses lining the neck and the inside of the papilla. 
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