NORTlt AMKRICAN PA RAsI'llC KXOASCE.K. 



91 



■of the spore, which, beconiiiii;- elliplicah are abjohiled. More 

 may follow until the protoplasm is exhausted. From such 

 sprouts, in man\- cases, new sprouts develop until the ascus 

 may become so tilled by tliese conidial formations as to render 

 it impossible to determine the original number of spores. 

 Brefeld has suggested the division of the species upon the 

 basis of the number of spores. While eight may be regarded 

 as the typical number, and asci with a smaller number or with 

 conidial formations may be considered deviations from the 

 tvpe. nevertheless so frequent and wide variations occur in 

 even a single species, and these too have been observed in 

 such a number of species, that one must conclude that upon 

 tile number of spores or the development of ascus-contents 

 no argument for the classification of the species can be based. 

 I find the parasitic North American forms number 18 spe- 

 >cies. affecting 48 hosts, distributed as follows: 



I fungus species upon i species Sap/iidaccic. 



1 " '• 



6 " " 



2 ■• •• 



This tabular view illustrates the importance of the group 

 from an economic standpoint. Our valued shade trees suffer 

 severely and of the affected Rosaccic ten species are fruit trees. 

 The parasitic presence is manifested upon some hosts by 

 simple spots on the leaves, where, unless the^■ occur in size or 

 numbers suflicient to interfere with their phvsiological func- 

 tions, thev ma\' bring abcnit no serious results. The forni' 

 Jlaoiiiisiclhi potent ilhc ( Farlow ) Sadeb. serves as an example. 



Exoasfiis defonuaus (Berk.) Fuckel will serve to illustrate 

 the species causing destructive leaf and branch deformations; 

 the fungus excites increased activit\" in the host tissues, and 

 the unusual size and number of cells produce folds or arches, 

 giving a blistered appearance to the leaves, and twists them 

 into the familiar •• leaf-curl"' of the peach. Y^ung twigs and 



