ONTOGENY OF THE PHYLLOXERA GALL OF GRAPE LEAF

Abstract

TO THE INTRINSIC biological interest which attaches to the study of gall development, there is added, in the case of the grape phylloxera, an important economic consideration. Brief mention may be made of the extensive ravages of European vineyards in the latter part of the nineteenth century. The early identification of the agent as a root-infesting homopteran was attended by intensive research on its life history. Regarding this life history, one proposal of interest for the present work is that the radicole (root-infesting) and gallicole (leaf-galling) parasites are different forms of the same insect (Riley, 1874; Cornu, 1879) . In 1916, Dr. Harry Rosen described, in its broad essentials, the development of the gall of the grape leaf (Vitis vulpina L.) caused by Phylloxera vastatrix Planch. in the vicinity of Madison, Wisconsin. Using the same materials, a group of investigators currently is engaged in a more detailed study of the relationships surrounding gall formation. These materials are particularly suitable for gall study: throughout the normal growing season, new leaf primordia are produced continually; grape shoots may be kept growing the year round in a greenhouse; Phylloxera reproduction occurs through several generations during spring and summer and can go on indefinitely in a warm greenhouse; reproduction of the gall-former does not involve sexuality (some investigators have questioned the existence of a male gallicole) ; and the gall structure is relatively simple (i.e., it is a kataplasmatic gall in Kiister's [1911] sense of the term) . One investigation (Newcomb, 1951a) has dealt with respiratory relationships and terminal oxidase systems in the gall tissues as compared with normal leaf tissues. The present paper gives a detailed account of anatomical development of the phylloxera gall. MATERIALS AND METHODS.-Galled plants growing on the University of Wisconsin campus and in the entomological greenhouses were used for this study. Dr. N. C. Fassett identified the grape species as Vitis vulpina L. During 1949 and 1950, leaves of various ages were removed from near the growing ends of the shoots. Whole tips of shoots also were used for a determination of the relationship between leaf size and galling. The materials were killed in Navaschin's solution, dehydrated, and embedded following a modification of the technique of Rawlins and Takahashi (1947). Staining was accomplished with safranin and fast green. GROWTH OF THE NORMAL LEAF.-The early de-