PERGANDE — NORTH AMERICAN PHYLLOXERIN^. 23I 



ington, for quite a number of years and appears to be slowly but 

 gradually increasing. 



Judging from the appearance of the galls alone, one is tempted 

 to divide them into two or perhaps three distinct species, with 

 regard to shape, size and color. A careful study, however, and 

 comparison of the migratory forms of their architects, have con- 

 clusively convinced me that the different forms of these galls are 

 nothing else but varieties of one species, depending, as it appears, 

 on the earlier or later settling of the young lice, and the there- 

 with connected more or less advanced stage of development of 

 the young leaves. There can be no doubt that the larger and 

 more brilliantly colored galls are the product of such of the 

 young lice of this species which hatched in advance of the bulk 

 of the same brood, just at the time when the development of the 

 leaves was most rapid and the circulation of the sap most vigor- 

 ous. To enable the future student, therefore, to recognize these 

 different forms more readily, it is deemed expedient to figure 

 each form of gall and to give each of them a variety name. 

 All these forms are usually, at least in this locality, met with at 

 about the same time and upon the same trees, though the two 

 largest or more brilliantly colored galls are much scarcer than 

 those of the typical form. As a rule, there is generally but a 

 single gall on a leaflet, though occasionally two, or even as many 

 as five or six, and in one instance even as many as twelve were 

 observed upon a single leaflet, all crowded together near the base 

 of the leaf, and more or less confluent. If there be more than 

 one on a leaf, it will be observed that generally most of them are 

 dwarfed, whilst but one or two have attained their full size. 



At what date the young stem-mother settles down has not 

 been ascertained, though it must be at the time when the young 

 leaves begin to unfold, at about the middle or latter part of April, 

 for it was observed that by the 20th of May many contained 

 already pupae, and a few even some winged insects, whilst others 

 contained only eggs and larvae. By the 15th or 20th of June 

 most of the galls are empty and by the end of the month all 

 inmates have left and the galls become dry and shrivelled. 



