1921] MILES—LEAF SPOTS OF ELM I7!I 
channel throughout its entire length which becomes the ostiole. 
This channel is lined with periphyses or hairlike structures which 
are hyphal outgrowths of the inner or lining layer of cells. These 
periphyses all point in a direction outward from the perithecial 
cavity, and so form a one-way passage from the spore bearing 
portion to the outside of the leaf. As the development of the 
beak nears completion, each layer of cells, whose increase has 
brought about its elongation, produces at its lower end one or 
more of these periphyses to each cell, so that the lower end or 
outer opening of the-ostiole is surrounded by a considerable brush 
of them. These later stages of the development of the ostiole are 
.seen in fig. 1, which shows two perithecia in an almost mature 
condition. The beaks are slightly longer than normal at this 
stage of maturity, but in all other respects the perithecia are 
typical. No further elongation of the beaks occurs until the 
ascospores are fully mature and ready to be discharged, sometime 
in the early spring, at which time they again begin growth and 
continue until they have just broken’ through the lower epidermis. 
In this stage, which is the condition in which they pass the winter, 
the lower end of the beak is still within the leaf tissue and merely 
pushes out the lower epidermis in the form of a hump or ‘tubercle. 
In the spring, when they have just broken through, these beaks, 
although short, are quite conspicuous on account of their fresh 
dark brown or almost black color. 
The asci in the figure last referred to are not yet mature, and 
it will be seen that the pseudoparenchyma is still present. This 
tissue is composed of small hyaline cells, filled with a very dense 
granular protoplasm, and with very thin walls; in fact, the walls 
are little more than membranes. It occupies the entire central 
region before the development of the asci, which grow out into it, 
and apparently it is used up by the asci in their growth, as no 
crowding of the tissue is apparent ahead of them. Such an inter- 
ascicular pseudoparenchyma has been described by STEVENS (35), 
who used it as the basis for the formation of a new genus, Desmotas- 
cus. He considered it an instance of delayed dissolution of the 
pseudoparenchymatous «central region of the developing peri- 
thecium to form the central cavity, and suggested that, since this 
