22O 



DISEASES OF CULTIVATED PLANTS 



Differs from Sphaerella in the spores being more than i -sep- 

 tate, and from Leptosphaerella in the absence of paraphyses. 



The majority of species occur on fallen leaves and are 

 considered as saprophytes, but nothing certain is known of 

 the life-history of most forms. 



Yew leaf scorch (Sphaerulina taxi, Massee) is at times 

 the cause of serious damage to yews. The leaves are 

 attacked, the first indication of mischief being a change from 

 the normal dark green to a brown colour. At a later stage 

 the upper surface of the leaf is densely studded with minute 

 pustules or warts, corresponding to the embedded perithecia, 

 the mouth alone protruding through the ruptured epidermis. 

 As a rule when this parasite once attacks a tree it spreads 

 very rapidly, so that within a short period of time all the 

 leaves have fallen ; many of the younger shoots are also 

 killed and fall to the ground. 



FIG. 63. i, Sphaerulitiataxi, on yew leaf, slightly 

 mag. ; 2, section of perithecium, slightly mag. ; 

 3, ascus containing spores, highly mag. ; 4, free 

 ascospores, highly mag. 



If the disease attacks a tree for two or three years in 

 succession it is usually killed outright. 



Fortunately this is not a common disease, or at all events 

 it is not very frequently recorded. I have seen it at work in 

 Cornwall, and also in Yorkshire, where a number of fine 

 yew-trees growing in a churchyard were being killed. 

 Mr. F. Moore of Glasnevin informed me that he had noticed 

 the disease in three counties in Ireland. 



