ASCOMYCETES 1 85 



IV. WITCHES' BROOM OF THE CHERRY 

 Exoascus Cerasi Fuckel 



This fungus is very common on both Primus avium and Primus 

 Cerasus in Europe. It has been reported infrequent in this country. 

 The mycelium attacks the branches, and the stimulation due to its 

 presence results in the formation of numerous twigs somewhat in 

 the form of a loose broom (Fig. 68). According to some observers 

 the twigs may be slightly thickened, although others claim that 

 there is no abnormality in the latter. The leaves on affected twigs 

 are also penetrated by the mycelium and they become somewhat 

 reddish and wrinkled or crumpled. The asci develop upon the 

 leaves, and measure, according to Sadebeck, 35-50 x y-io/j. (25- 

 33 X 6-9 in specimens studied by Atkinson). During the flowering 

 period of Primus Cerasus the witches' brooms are very conspicuous, 

 since the broom usually bears leaves only. 



Prevention in this case requires the destruction of all affected 

 branches, as well, probably, as a thorough spraying about the time 

 the asci are mature, and a subsequent one when the buds swell 

 the following spring. 



Of the many other species of Exoascus the majority are para- 

 sitic upon different species of Prunus, while Alnus, Populus, Acer, 

 yEsculus, Carpinus, Crataegus, Pyrus, Quercus, Ulmus, and other 

 plants are also hosts. 



V. HELOTIACEjC 

 The Helotiaceae are Discomycetes of which the fruiting body is 

 a distinct apothecium or cup. In texture these fungi may vary 

 from wax-like to a rather tough consistency. The body is at first 

 almost spherical and nearly or quite closed. With growth and dif- 

 ferentiation it opens into the characteristic cup, sessile or supported 

 by a stalk varying in length in different species. The sterile tissue 

 of the cup is pseudoparenchymatous. The cylindrical asci arise 

 from a hyphal-like hymenium, and each ascus contains eight spores. 

 At maturity the ascus opens at the apex and forcibly ejects the 

 spores, the latter being hyaline, diverse in form, and 1-8 celled. 

 Filamentous paraphyses are present. Sclerotinia and Dasyscypha 

 may be mentioned as containing parasitic species. 



