GALLS CAUSED BY MITES 103 



the other plants, with the result that the majority of their 

 flowers were double, as well as those of isolated plants on 

 which he had placed mites. He remarks: " Veronica officinalis 

 has only two stamens in each flower, and in the double 

 flowers both these and the two carpels are changed into 

 petals, so that of course we could not expect fruit and seeds 

 from them. It would not be impossible, however, that 

 flowers of other plant families, which are provided with a 

 large number of stamens, might behave differently. It 

 might happen, for example, that only some of the stamens 

 would be changed into the petals by the gall-mites, and that 

 the carpels would remain capable of fertilization. If on 

 such plants fruits and seeds capable of germination should 

 ripen, the latter might perhaps produce plants with com- 

 pletely and half double flowers. This would be explained 

 by supposing that the alteration undergone by the proto- 

 plasm of the cells in the outer part of the flower had ex- 

 tended to the inner, especially to the ovules and seeds, and, 

 further, to the plants proceeding from these seeds. I would, 

 therefore, not undertake to state that the Stocks {Matthiola 

 annua and incana), the Wallflower {Cheiranthus ckeiri), the 

 Pinks (Dianthus caryophylltis, plumarius, etc.), the Poppies 

 (Papaver Rhoeas and somniferum), various Ranunculaceae 

 (Delphinium, Poeonia, Ranunculus), and many other plants 

 which have long been cultivated in gardens with semi- 

 double flowers, and which produce such flowers when pro- 

 pagated by seeds, had not gained this characteristic in the 

 first place by the influence of gall-mites." 



Economic Notes 



Two species of mites cause mucb damage in fruit gardens. 

 The more troublesome is probably the Black Currant gall- 

 mite, Eriophyes ribis Nalepa. It was observed in this 

 country at least sixty years ago, but it is only within recent 

 years that it has spread rapidly and become a serious pest. 

 These mites shelter in the buds over winter and migrate in 



