preposterous Jordanon of botanical literature, may best be acquired by field experience with a group of related organisms. For illustration we may again utilize Cynips erinacei and some of its close relatives as they occur in the eastern portion of the United States.
We have already described erinacei as a highly variable species occurring on the leaves of the white oak, Quercus alba, over a tremendous area chiefly in the northern Middle West. On almost all of the infested trees at any locality in this area one may find a mixture of smooth and spiny galls of every extreme and intermediate type. Often all types of galls are crowded onto a single leaf, but occasionally a particular tree will have a preponderance of one type, and on several occasions we have found isolated trees well covered, as far as we could discover, with galls of only a single extreme type. These peculiar colonies, however, have always been on isolated trees or groups of trees, and they would appear to represent Mendelian races in which homozygosity in regard to particular characters had been affected by the isolation of the colony. Subsequent examinations of insects from such galls have failed to indicate that these local populations are homozygous in regard to any of the other characters that might vary within the species, and such colonies are passed by the taxonomist as ephemeral entities not satisfying the species concept.
If one will extend his collections in the first locality to a number of trees scattered over any appreciable distance—several hundred yards or a mile or two—he will leave the region with a sample that is as variable but as uniform as we have described it. If one travels to a second locality, five miles or fifty miles or a hundred and fifty miles from the first, the first collections may be duplicated. If one continues this procedure day after day, over the thousands of square miles which are the range of erinacei, one must become impressed with the fact that this is a population of inconceivably great numbers of individuals that are in certain aspects different and yet in an essential way similar over this tremendous territory. Of course, we can take only scant samples of the population, and we are reduced to glancing at most of the trees with their thousands of galls which we have no time to gather; or we fall to wondering how many inconceivable millions of individuals of erinacei there are on all the trees
