164 



ASCOMYCETES. 



may bear several brooms, 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 removal 

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



recommended. 



[According to Shirai (Tokio 

 botanical magaziTie, 1895) witches' 

 brooms are produced in Japan 

 on Fncnus pseudo-cerawiis, by a 

 distinct species, Ex. pseudo- 

 cerasus.] 



Exoascus minor Sad. This 

 species induces hypertrophy of 

 shoots of Prunus Chamaccerasiis 

 and P. Cerasus, but cannot be 

 said to cause formation of 

 witches' brooms. The mycelium, 

 hibernates in the buds, and 

 spreads only underneath the 

 cuticle, while that of JEx. cerasi 

 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 

 be attacked, while their neigh- 

 bours remain quite healthy ; both 

 ilowers and fruit may also be 

 borne. Diseased leaves appear much crumpled, and Sadebeck 

 states they have an odour of cumarin ; they turn brown pre- 

 maturely and fall off. 



Exoascus insititiae Sad. is found on Pi-unus domestica and 

 P. Insititia in Europe, and P. pennsylvanica in North America. 

 It 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. cerasi, in the bark 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. 



Fig. 59. — Twig from witches' broom in 

 foliage, as in Fig. 57. Photographed at same 

 time as Fig. 58 for comparison, (v. Tubeuf 

 phot.) 



