GALLS INDUCED BY PLANT-LICE 85 



and within the roll her numerous progeny go through 

 their moults. The adults fly to other trees, and there 

 deposit their remarkable progeny. Buckton* observes: 

 " These young are born in the form of yellow ova, and 

 might be almost mistaken for such, except from the existence 

 of two black eyes which are sufficiently perceptible. The 

 casting of a delicate membrane permits the disengagement 

 of the limbs and the rapid growth of a golden-yellow pilose 

 coat." The fourth and fifth generations are active wingless 

 creatures, which live on the twigs and powder the leaves 

 with wool. The sixth generation are winged insects, which 

 differ from the early Alatae in their smaller size. They fre- 

 quent the bark, and there give rise to the seventh generation, 

 in which both sexes are present, the male being very 

 diminutive. The female lays a single egg, which produces 

 the hibernating Fimdatrix. 



The remarkable tumours or " cankers " not infrequently 

 seen on Apple trees are always associated with Myzoxylus 

 laniger (Schizotteura lanigera), the so-called "American blight.'' 

 Descriptions of the insect and its life-history may be found 

 in Miss Ormerod's " Manual " and other books on economic 

 zoology. The structure and origin of the canker has been 

 investigated by Dr. J. E. Blomfield. The deformities are 

 produced on the roots as well as the stems and branches. 

 The Aphidae do not attack the green terminal part of a twig, 

 but select a spot near to the old wood, where the formation 

 of a periderm is indicated by the reddish-brown tint. Great 

 activity of the cambial region immediately takes place, and 

 overgrowth results. The soft parenchymatous tissue splits 

 in dry weather, and fungi enter, causing necrosis and 

 ulceration, which the plant tries to heal by producing new 

 cambial tissue. If this continues long, tumours attaining 

 the size of a man's fist may arise. A striking example of 

 the latter condition is shown in Plate XI., which depicts 

 part of the branch of an Apple tree bearing thirteen spherical 

 tumours, the smallest being about the size of a pea, the 

 • "British Aphides," vol. iii., pp. 98, 99. 



