84 PROCEEDINGS OF THE AMERICAN ACADEMY 



latter is eight-spored, but the former is polysporic, not to mention 

 other differences. Ex. flaviis forms circumscribed yellow spots on the 

 leaves during the month of June. The asci are borne between the 

 cuticle and the epidermis, the cells of which become somewhat de- 

 pressed as the fungus develops. The asci are very obtuse, often being 

 nearly rectangular when seen in section, and they are very densely 

 packed together. The mycelium, which is not easily seen except in 

 thin stained sections, extends between the cuticle and epidermis, and, 

 making its way between the cells of the latter, winds amongst the sub- 

 epidermal parenchyma, but does not extend through the central part 

 of the leaf. In sections, one sees the base of the asci abruptly drawn 

 out into a short process, which is wedged in between the epidermal 

 cells connecting with the mycelium below. It will be seen that the 

 species occupies a position between the genus Taphrina,Si?, represented 

 by T. aurea, where the asci are polysporic and end in rootlike ex- 

 tremities which jiass down between the epidermal cells, and the 

 genus Exoascus, as represented by Ex. Prani, where the asci are 

 eight-spored and the mycelium is found throughout the leaves. Our 

 species, however, is more nearly related to Taphrina, and the name 

 should be changed to Taphrina jlava. 



Taphrina flava Farlow. Mycelium between the cells of the 

 outer part of the leaves. Asci on both sides of the leaves, between 

 the cuticle and epidermis, densely packed, obtuse or truncate at both 

 extremities, 38-57/x long by 20-23/a broad. Spores very numerous, 

 bacterioid, hyaline, 3-7/a long by 1.5-2/x broad. 



Forming bright yellow spots on leaves of Betula alba. Newton, 

 Mass., June. 



No. 298. I am unable to distinguish this form on Primus serotina 

 from the larger form on cultivated plums. An Exoascus, which is 

 apparently the same as Ex. Wiesneri Eathay, is not unfrequently 

 found with No. 298. It produces swellings and curling of the 

 leaves, and enlargements of the younger twigs, recalling the deformi- 

 ties produced on peach leaves by Ascomyces deformans. The form 

 of Prunus leaves which, as I have said, is j^robably Ex. Wiesneri (^Ex. 

 deformans f. Cerasi Fuckel), is common with us, but the distortions 

 are not as marked as those figured by Rathay. The specific determi- 

 nation of the forms on leaves of Rosacece is difficult, and in No. 299 

 is a form on Potentilla Canadensis which was distributed under the 

 name of Ex. deformans var. Potentillce. The form is very common in 

 Eastern Massachusetts, and is found during the whole summer, but 

 especially in the latter part of June and July. It first appears as 



