THE FUNGI WHICH CAUSE PLANT DISEASE 127 



Subgenus. 2. Eutaphrina,— one series (Betula) 



Asci broadly cylindric, rarely contracted at the base or from 

 the middle down, truncate above and sometimes in-sunken. On 

 Amentaceae, chiefly Betula, Alnus, Ostrya, Carpinus, Quercus, 

 Populus. Of the twenty-four species of this series but few are 

 of importance. 



T. coerulescens (D. & M.) Tul." Annual, producing blisters 

 on the leaves of oak, the sporing surface bluish; asci elongate, 

 broadly cylindric, 55-78 x 18-24 m; spores breaking up into 

 conidia. 



On various species of Quercus in Europe and America. 



T. ulmi (Fcl.) Joh., on the elm; T. aurea (Pers.) Fries on the 

 leaves of Populus and T. johonsonii Sad. on the fertile aments of 

 the aspen are among the more important remaining species of the 

 series. 



Subgenus 3. Exoascus, — ^two series 



Asci clavate, normally cylindric or more or less abbreviated. 



(1) Prunus series on Rosacese. Asci slender, clavate, narrowed, 

 below, broadest in their upper fourth, varying through all inter- 

 mediate forms to narrowly cylindric. 



(2) iEsculus series, on Sapindacae, Anacardiaceae, etc. — ^Asci 

 broadly cylindric, short, rounded or truncate. 



The more important economic species of the genus belong to 

 the Prunus series. 



T. deformans (Fcl.) Tul.^' ^'^' " 



The irregular vegetative mycelium devoid of haustoria grows 

 in the leaf parenchyma and petiole and in the cortex of branches. 

 A distributive mycelium lies close beneath the epidermal cells of 

 twigs and in the pith and extends some distance through the twig. 

 Fig. 87. Branches arise from the vegetative mycelium, penetrate 

 between the epidermal cells to the cuticle and then branch freely 

 to form a network of short distended cells beneath the cuticle. 

 This is the hymenium, a layer of ascogenous cells. These cells 

 elongate perpendicularly to the host's surface, Fig. 85, rupture 

 the cuticle, and form a plush-like layer. The protoplasmic con- 



