172 Robinson . — Notes on the Genus Tctphrina. 
than on the under surface of the leaf, vary from 20-30 /x in 
length, and are often less than 2 /x thick. The spores are 
eight or many, 3-4 /x in diameter. 
T. FLAVA, Farw., in Proceedings of Amer. Acad. vol. 
xviii (1883), p. 84. 
Exoascus Jlavus , Farw., Ellis’ N. A. Fungi (1879), 
No. 300. 
This species must be carefully distinguished from the 
more recent and very different Exoascus jlavus of Sade- 
beck, which Johanson, with deference to the priority of 
Dr. Farlow’s name, has called Taphrina Sadebeckii. T. jiava , 
Farw., is also quite distinct from Exoascus Betulae , Fuckel, 
which also occurs in roundish spots on the leaves of various 
species of Betula , but has not, to my knowledge, been found 
in America. If it does occur here it may be distinguished 
from T. jiava by its shorter and more slender asci, its well- 
developed stalk-cells, and the absence of any subepidermal 
mycelium. 
T. jiava, Farw., has been found most often on Betula alba , 
var. popidifolia , Spach., in Eastern Massachusetts and New 
Hampshire, but has also been collected on Mt. Washington, 
N. H. (E. Faxon), on B. papyracca , Ait. It appears on the 
leaves of either host in June as bright yellow, circular spots, 
which vary considerably in diameter. In some dried material 
examined these spots were distinctly concave above and 
convex beneath. The asci are very numerous and densely 
packed together on both sides of the leaf. In outline they 
are rectangular, being truncated at each end ; their length is 
31-52 /x, and thickness 17-26 /x. Within each ascus there is a 
great number of very small oblong spores. The asci have no 
proper stalk-cells, but in a thin section the subepidermal 
mycelium (hymenium) is seen to be connected with the asci 
by very slender pedicels which pass vertically upward between 
the cells of the epidermis and expand abruptly into the 
asci above. When the upper portion only of such a pedicel 
is seen, it may appear like a downwardly directed process 
