164 



ASOOMYCETES. 



may bear several bruuins, and every tree in a fruit-garden 

 may be attacked, so that this disease has assumed consider- 

 able economic importance. As a preventive measure, the remo^'al 

 of all brooms at the time of pruning the trees is strongly 



recommended. 



[According to Shirai (Tokio 

 Jititcmical magazine, 1895) witches' 

 brooms are produced in Ja})an 

 on Primus i^scvdo-ccrasvs, by a 

 distinct species, Ex. ^«r;/^(>- 

 ccra^us.'l 



Exoascus minor iSad. This 

 species induces hypertrophy of 

 shoots of Prunus Chamaccrra.Kns 

 and P. Ccrasi's, but cannot be 

 said to cause formation of 

 witches' brooms. The mycelium 

 hibernates in the buds, autl 

 spreads only underneath the 

 cuticle, while that of Mr. cor/si 

 lives in the tissue of the twigs 

 and leaves. It is characteristic 

 of this species that only leaves 

 here and there on a twig may 



Fig. 5!).-Twig from witches' broom in bc attacked, whilc tlicir ncigll- 

 foliage, as in Fig. 67. Pliotographed at same . ' 



time as Fig. .OS for comparison, (v. Tubeuf bours remain quitc healthy; both 



flowers and fruit may also be 

 borne. Diseased leaves appear much crumpled, and Sadebeck 

 states they have an odour of cumarin ; they turn brown |)re- 

 maturely and fall off. 



Exoascus insititiae Sad. is found on Prunvs domcstica and 

 P. Insititia in Europe, and P. 2J<^nnsylvanica in North America. 

 Tt causes formation of witches' brooms smaller than those on 

 the cherry tree, yet probably more common in the fruit garden. 

 They bear no fruit, and are a source of considerable loss. 

 The mycelium hibernates, like that of Ex. ccrasi, in the Itark of 

 twigs, and spreads in spring into the buds. 



The leaves of the host bear asci on the lower epidermis ; 

 they are always more or less curled up, and fall off early. 

 To prune off all brooms is the best preventive measure. 



