Ascus Dehiscence in Lecanidion Atratum and its Significance

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Abstract
SUMMARY Lecanidion atratum, which has been placed with the inoperculate Discomycetes, has a method of spore discharge unique for that group. The outer ascus wall breaks at, or near the apex and rolls back; an inner membrane, here termed the endoascus, pushes up above the epithecium nearly one-third the length of the ascus; the spores are then shot out successively and forcefully from the apex of the projecting endoascus. This endoascus type of dehiscence is characteristic of certain Pyrenomycetes, but has not before been reported in any of the Discomycetes. On the basis of this character, which is considered a reliable indicator of relationships, the Patellariaceae seem to show a closer relationship with certain Pyrenomycetes than with the other inoperculate Discomycetes. It may also prove to be an additional criterion of value in determining the natural classification of the inoperculate Discomycetes and disco-lichens. The writer is greatly indebted to Dr. F. J. Seaver for the collection of living material that made this study possible, and for his generous assistance with the preparation of the manuscript.

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