.q5 north AMERICAN PARASITIC EXOASCE.-E. 



these cells swell uniformly in the course of further develop- 

 ment and become, either immediately or after a further divi- 

 sion and individualization, ascogenous cells, which, for the 

 most part, stand closely pressed against one another and form 

 a sub-cuticular fruit-bearing layer or hymenium. The sub- 

 cuticular mycelium is used up completely in the formation of 

 'the ascus. The disease affects either branches or branch sys- 

 tems, and therefore, through the influence which the parasite 

 •exerts, a more or less considerable hypertrophical deforma- 

 tion in the leaves and also in part of the stem is produced. 

 Pocket-formations in the floral envelopes, and the witches' 

 broom ( in the widest sense of the words ) on leafy twigs are 

 the appearance of disease b^■ which this genus is charac- 

 terized. 



A. The mycelium is perennial in the inner tissue of the 

 organs of the stem and at the time of new vegetative growth 

 sends out its branches into the developing leaves. These 

 branches spread themselves out in the inner tissues and 

 thence take the first steps towards the formation of a sub- 

 cuticular hvmenium. 



1. The de\'elopment of the hymenium occurs only in the 

 tloral envelopes of the host-plant, pocket-formations. ( Tas- 



■chenbildungen ). 



Asci with stalk-cells: 



£xoasciis pniiii Fuckel. 

 E.xoascuS' cummuiiis Sadeb. 

 Exoascus farJozvii Sadeb. 



2. The dcN'elopment of the hymenium occurs onlv in the 

 foliage leaves of host-plant. •• Witches" broom "' forms. ( Hex- 

 enbesenbildungen. i 



a. Asci with stalk-cells. 



Exoasctis ccrasi ( Fuck. ) Sadeb. 



b. Asci without stalk- cells. 



Exoascus fiirpnrasccus (Ellis & Everhart ) Sadeb. 



