PEAR LEAF BLISTER 91 



appearance year by year depends entirely on the host- 

 plant being infected by spores floating in the air, or carried 

 by some outside agency. Collecting the diseased leaves 

 from large trees is not practicable ; but this is an easy 

 matter, and well worth the trouble, in the case of nursery 

 stock, and is the most certain means of stamping out the 

 disease. Spraying with dilute Bordeaux mixture two or 

 three times, at intervals of a fortnight, until the leaves are 

 full grown, holds this, and many other pests, in check, 

 which are otherwise always ready to attack, and con- 

 sequently retard the growth of, young trees. 



The following species of Taphrina also occur in Britain. 

 If such become a nuisance, the preventive means suggested 

 under Taphrina bullata will be found adequate: — 



ALDEB LEAF BLISTER 



(Taphrina sadebeckii, Johans.) 



Forms small white or yellowish patches on the under, 

 less frequently on the upper, surface of the leaves of 

 alders. 



POPLAR LEAF BLISTER 



(Taphrina aurea, Fries.) 



Forms large golden-yellow blisters, concave on the 

 under surface of the leaf, convex on the upper surface, on 

 the leaves of different kinds of poplar. 



