INTERNAL AECIA 
Frederick A. Wolf 
(With Plate hi) 
Among the heteroecious rusts whose hosts grow in swampy 
situations is a form whose telial stage appears on species of 
Scirpus and whose aecial stage is developed upon one of the mints, 
Lycopiis virginicus L. This rust, Piiccinia angustata Peck,^ is 
very abundant, during the month of May, in the vicinity of 
Auburn, Ala. The aecial sori may appear upon the stems, petioles 
and leaves, resulting in the hypertrophy of affected tissues. The 
enlargements upon the stems and petioles seem always to be more 
prominent than those upon the leaves. It was found upon sec- 
tioning the sori, which occurred upon both stems and petioles, that 
many of them not only possessed aecia which, upon dehiscence, 
liberate their spores to the exterior of the host, but also those 
which were entirely internal. In case the affected portions of the 
host are quite mature the pith cells will have disintegrated, causing 
the stem to be hollow, and the aecia then open into this cavity. If 
petioles or younger portions of the stem are affected, certain of 
the pith cells are broken down and the cluster cups open into the 
surrounding parenchyma tissue. As far as can be observed these 
internal cluster cups are similar in origin, structure, size and form 
to those which are erumpent at maturity. Masses of fungous 
tissue are present in certain places in which the aecia occur and 
the mycelium more or less densely ramifies throughout adjacent 
host tissues. These internal aecia may be so numerous that three 
or four will be present in a section ten micromillimeters in 
thickness. 
The formation of aecia is usually subepidermal and when they 
are ready for anthesis they break through the epidermis. In the 
1 For this determination thanks are due Dr. J. C. Arthur, of Purdue 
University. 
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