1910) HEALD & WOLF—STRUCTURE OF URNULA GEASTER 185 
the normal cause of the expulsion of the spores, the same phenomenon 
may be induced by the release of tension due to breaking the rays. 
After the spores have been expelled, the release of the tension in the 
hymenial surface causes the segments of the apothecium to be raised 
and curled inward (text fig. 2). 
IG. 2.—Apothecia of various forms, showing origin from roots and the manner of 
dehiscence. 
The wall of the apothecium is thick, reaching 3.5™™ in many 
cases. The original description does not specify the thickness, while 
KuPrER® gives 2. 5™™ as the extreme measurement. This difference 
may be explained easily by the fact that only dry material was avail- 
able in all the previous studies. 
The wall of the apothecium shows in section a region of brown 
hairs, about o.1™™ jn thickness, which is the cause of the brown 
tomentose exterior. Just below the hairy layer is a relatively narrow 
Cortical zone made up of densely interwoven hyphae, while the remain- 
* Kuprer, E. M., Bull. Torr. Bot. Club 29:143. 1902. 
