THK PARASITIC EXOASCP^AE. 



16T 



Exoascus coerulescens (Mont, et Desm.) produces similar 

 blisters on oak leaves. 



Fig. 63. — JExoctscus aureus. Leaf section from the margiu of a swelling, showing 

 normal and hypertropbied tissue. The cells of the swelling are abnormally 

 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. Tubeuf del.) 



Exoascus cameus Johan. occurs on leaves of Betula odorata, 

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



Fig. 64. — Exoascus cai-neus on Betula odorata. (v. Tubeuf del.) 



Fig. 65.— Section of normal leaf of Betula 

 odorata. (After W. G. Smith.) 



Fig. 66.— Section of leaf hypertropbied by 

 attack of Exoascus carneus ; the asci of the 

 fungus coat the upper epidermis. Drawn 

 with the same magnification as Fig. 65, for 

 comparison. (After W. G. Smith.) 



