Excerpt from The Life History of Two Species of Plant-Lice: Inhabiting Both the Witch Both the Witch-Hazel and Birch

What becomes of this particular species during the intervening time after leaving its gall remained a profound mystery to the writer for many years, notwithstanding continuous efforts to solve the problem.

Accidentally, while on a. Collecting trip near Tacoma, D. C., in Sep tember, 1890, the writer observed a peculiar Aphid inhab.ting the under side of the leaves of a small shrub of Betula nigra, but failed at that time to recognize it as the missing link of Hormaphis. During the following seven years nothing additional was discovered to cause me to continue observations, this being due in a great measure to the destruction of large numbers of witch-hazel bushes and young birches, and the consequent scarcity of galls in the woods surrounding the city of Washington. Fortunately, however, I discovered in September, 1897, a number of witch-hazel trees and bushes, as well as young birches, in a narrow and protected valley near the edge of a small creek at Cabin John Bridge, Md., where I found numerous old anddry galls on the leaves of the witch-hazel. Here I began again my search for the evading generations of this species, and in examining the leaves of birches rediscovered on many of them the same peculiar Aphid which had previously been found at Tacoma. It was in various Stages of development, including the winged migrants, which proved, after a thorough examination and comparison with the Spring migrants of the witch - hazel, to be identical with Hormaphis hama melidis. To be sure of no mistake an examination was made of the leaves of witch-hazels near the birches with the result that the under side of numerous leaves was found to be almost completely covered with larvae of various stages, and among them numerous specimens of the migrants from birch, actively engaged depositing their progeny, which later on proved to be the sexual generation. This settled the previously obscure question as to the secondary host of the interme diate generations, and enabled me to continue and to complete my prctracted observations of the life history of this remarkable little species and the strange transformations it undergoes on the birches which will be recorded in the following pages.

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