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fact that the mites, when the buds expand, crawl from the scale leaves 

 into the young developing shoot and puncture the delicate tissues of 

 the still folded leaflets, the petioles and the main axis. The continuous 

 suction causes large, raised and often confluent blisters on both upper 

 and under surfaces of the leaves. The petioles of the leaves and the 

 young main axis show the same malformations. All parts of the fruit 

 blossom are deformed in the same way and fruit in consequence fails 

 to set. When the leaves expand the mites still continue to perforate 

 the tissues until, after a bad attack, the whole leaf surface, the veins 

 and the petiole become covered with succulent outgrowths. These 

 excrescences, besides giving a plentiful supply of food material, afford 

 the mites a means of protection. The bases of the ribs of the leaves 

 especially are surrounded by a mass of these outgrowths, and beneath 

 them are found colonies of mites, nymphs and eggs. Leaves so attacked 

 are considerably below the normal size, and the main stem is reduced 

 in length. The leaf colour is yellow-green, and the tree has an unhealthy 

 appearance. As the season advances the leaves harden and these 

 excrescences lose their watery contents and become dry and discoloured. 

 The injured epidermis frequently cracks and the injured bark splits 

 and comes away from the stem. Practically all the injury done to 

 the vegetative portions of the gooseberry occurs in the spring and 

 early summer when the trees are making active growth. Later in the 

 season the texture of the leaves becomes tough, new growth is made 

 slowly and hardens quickly and the mites find a difficulty in obtaining 

 a food supply. Therefore, when the buds of the current year's growth 

 are large enough for the mites to enter, they are found to collect in the 

 scale leaves and it is in this position that their life-history is completed. 

 The difference in the method of migration of Eriophyes on black 

 currant and on gooseberry is due to the fact that the gooseberry buds 

 are not killed. Shoots develop normally from them, the mites have 

 their food at hand and it is unnecessary for them to adopt a uniform 

 migratory action. A comparison of the number of mites present at 

 different stages of their life-history on the two host plants, R. nigrum 

 and R. grossularia, shows that, before migration takes place in spring, 

 the number of mites on black currant is countless, while a few hundreds 

 only are to be found on the scale leaves of the gooseberry. A few weeks 

 after the buds have expanded, the mites on the gooseberry have 

 innumerably increased, while only a few can be found in the leaf bases 

 of the black currant. Nor does the mite on the black currant appear 

 to be numerically so strong as that on the gooseberry until the new 

 buds are entered, when a phenomenal increase takes place. The mite 

 on the gooseberry, on the other hand, appears to receive a check to 

 reproduction when the buds are entered. The check to the increase 

 of the mites on the black currant at the migratory period is undoubtedly 

 due to the excessive loss of life caused by the hazardous method of 

 distribution, whilst that on the gooseberry ensures the safe arrival of 

 most of the mites. The distribution of E. ribis on R. grossularia 

 appears to be as universal as on R. nigrum, and most orchards are 

 infested, although symptoms of attack are not always conspicuous. 

 The black currant is so badly crippled after a serious attack that it is 

 of little use to the grower ; the gooseberry has its growth checked 

 early in the seaGon, but recovers later on ; R. rubrum (the red currant) 

 appears to be the least injured. 



(C161) c 



