The best proof is afforded by the varieties which grow wild in localities where they are quite isolated from the species, and where for this reason, no possibility of crossing disturbs the significance of the proof. As one instance the rayless form of the wild camomile, or the _Matricaria Chamomilla discoidea_ may be mentioned. Many systematists have been so strongly [157] impressed with its absolute constancy and its behavior as an ordinary species, that they have elevated it, as it is called, to the rank of a species. As such it is described under the name of _Matricaria discoidea_ DC. It is remarkable for its rapid and widespread distribution, as of late years it has become naturalized in different parts of America and of Europe, where it is to be seen especially in France and in Norway. Experimentally I raised in succeeding years between 1000 and 2000 seedlings, but observed no trace of reversion, either in the strongest or in the numerous very small and weak individuals which appeared in the cultures. The tansy-ragwort or _Senecio Jacobaea_ may be chosen as a second instance. It is a perennial herb with short rootstocks and stout stems bearing numerous short-peduncled heads in large compact corymb; it multiplies itself abundantly by seeds and is very common on the sand dunes of Holland. It has two forms, differing only in the occurrence or the lack of the ray florets. But these two varieties occupy different localities and are even limited to different provinces. As far as I have been able to ascertain on numerous excursions during a series of years, they never sport, and are only intermingled on the outskirts of their habitats. The rayless form is generally considered as the [158] variety but it is quite as stable as the radiate species. The radiate varieties of marigold, quoted in a former lecture, seem to be equally constant, when growing far away from their prototypes. I sowed the seeds of a single plant of the radiate form of _Bidens cernua_, and found all of the seedlings came true, and in the next year I had from their seed between 2,000 and 3,000 flowering individuals, all equally radiate. Many species of composites have been tried, and they are all constant. On the other hand rare sports of this kind have been observed by Murr and other authors. Many kinds of vegetables and of fruits give instances of stability. White strawberries, green grapes, white currants, crisped lettuce, crisped parsley and some other crisped forms may be cited. The spinage without prickles is a widely known instance. White-flowered flax never reverts to the blue prototype, if kept pure. Sugar-peas and sugar-corn afford further instances. Strawberries without runners have come true from seed ever since their first appearance, over a hundred years ago.