THE J'AHASITIC EXOASCEAE. 



167 



Exoascus coerulescens (Mont, et Desm.) produces similai 

 blisters on oak leaves. 



Fici. 6'i.—Ej:o((scv.s aurevs. Leaf section from the margin of a swelling, showing 

 normal and hypertrophied tissue. The cells of the swelling are alniomially 

 elongated with thickened walls, and some show secondary cell-division. The 

 bases of the asci are wedged in between the cells; one ascus is shown with 

 conidia. (v. Tubeiif del.) 



Exoascus cameus Johan. occurs on leaves of Betula o'loralu, 

 B. ndua, and B. intermedia. The pustular outgrowths rise above 



nevs on Bitt'lo. odomto. (v. Tubciif del.) 



Fio. 6u.— Section of nonual leaf of Betula 

 odoratn. (After W. G. Smith.) 



Fn^. 00.- Section of leaf hypertrophied by 

 attack of Exooncus cameus; the asci of the 

 fungus coat the upper epidermi.s. Dmwn 

 with the same magnification as Fig. 6-0, for 

 comparison. (After W. G. Smith.) 



