Page:Phylogeny of cynipid genera and biological characteristics.pdf/20

 successful in reaching their full development and froim these the alternate, the agamic generation, will be produced. A further point of interest with this species is the fact that the adults of the two generations are very similar except in size, in mode of reproduction, and in the condition of the wings: although the agamnic females are always wingless and the males of the bisexual generation are winged, the bisexual females either have normal wings or have reduced wings, or are almost wingless, exhibiting in this as in other respects not well fixed and not very great differences between the alternate generations, even though at first sight the differences appear remarkable.

I have found inidications of the sami-e sort of incomplete fixation of the habits of a generation in our (ommnnon Am-erican species, Biorhiza forticornis. In the well-known formy the adults are wingless, agamic, and emerge in December, often during very cold weatheirwhen the ground may be coveired with sInow. These adults are very strongly geotropic, positively, and will runi downi the tree to the grouind, anid I have sueceeded in observing them oviposit in the roots oIr at the bases of the trunks of the white oaks. Though I have niot succeeded yet in obtaining galls from these eggs, it is quite certain that a root gall does form and that these develop the adults of the bisexual generation. But, about the middle of the March following the winter emiergence of the species, I found a second lot of wingless agamic femiales emnerging from the same galls which had given the first lot of agamic adults. The insects of the two lots were not to be distinguished except by a remarkable difference in sensory reaction: these early spring adults were negatively geotropic, as I thoroughly proved by careful experimneints. They climbed up the trees and oviposited in the termilnal buds. Although the tree grew nicely that spring, no galls developed from these eggs. Whether galls ever develop from eggs laid by these spring forms of agamic females I cannot yet say positively. It may be that here we have another instance of the sort described by Adler for Cynips pallida. It is not unlikely that the fixation of the nature of the second generation for some of the species was a matter of repeated trial, and that only after some forms had failed of survival did one forin finally reinain and become fixed as the alternate generation. We have no way of estimating how many instances of this sort are yet to be discovered, but it is also reasonable to believe that for some species there was little or no amount of trial before a form was found which could survive.