740 Horticultural Institute at Geisenheim. [dec, 



necessary to enter into technical details, but it may be men- 

 tioned that the problem was attacked by. carefully designed 

 field experiments, backed up by work in the laboratory. 



As soon as one begins to study plant diseases in Germany it 

 is apparent that they can be divided into three classes : (a) 

 Those common to England and Germany and of equal in- 

 tensity in both countries; (b) Those common to both countries 

 but worse in one country than the other; (c) Diseases that j 

 occur in Germany and which might be exported to England. 



The majority are of the first class, and their discussion is of 

 only technical interest. The second class includes many in- j 

 teresting cases, such as that of Anthonomus porno rum. This 

 insect, commonly called the Apple Blossom Weevil, does not 

 appear to do much damage in Germany, though in England 

 it is a pest that annually causes a large loss of the apple crops 

 in certain regions. The allied form, however, A. pyri, which 

 attacks the buds of pear trees, appears to be fairly serious, j 

 but does not occur in England. Other somewhat similar ex- 

 amples might be quoted. 



The third heading includes those diseases which have the 

 most interest for English growers. Of these, perhaps the 

 two most important are Diaspis fallax and Rhagoletis cerasi. 

 The former, a scale insect called die rote austernformige 

 Schildlaus, is an important disease of pears, especially of 

 espaliers. A native of the south, it came to Geisenheim and to 

 South- West Germany about thirty years ago. It is common 

 now in France, and has recently been reported from Holland. 

 It attacks the older twigs and boughs, and in fact any part of 

 the tree where cork formation has already taken place. It 

 also occurs on the fruit. The disease shows its virulence in 

 the sickly appearance of the trees and in characteristic depres- 

 sions or " eindellungen " in the large boughs. Both male and 

 female larvae, before secreting their true scale, are covered 

 with waxy thread, which renders them very easily transport- 

 able by the wind, and facilitates their spread throughout a 

 plantation. Diaspis fallax is essentially a southern scale 

 insect, and it is unlikely that it would thrive even if introduced 

 into England. Still it is an insect that should be looked out 

 for, since it is capable of inflicting severe injury under certain 

 conditions. 



