[170] Wherever this variety is cultivated the same reversion may be seen; it is produced abundantly, and even under seemingly normal circumstances. But as in the case of the _Ribes_ all the specimens are derived by buds from a single original plant. The variety was introduced from Japan about the year 1860, but is probably much older. Nothing is known as to its real origin. It never bears flowers or fruits. It is curious to note that the analogous variety of the European yew, _Taxus baccata fastigiata_, though much more commonly cultivated than the _Cephalotaxus_, never reverts, at least as far as I have been able to ascertain. This clearly corroborates the explanation given above. After considering these rare instances of more widely known reversions, we may now examine the question of atavism from a broader point of view. But in doing so it should once more be remembered, that all cases of hybridism and also all varieties sporting annually or frequently, are to be wholly excluded. Only the very rare occurrence of instances of atavism in varieties that are for the rest known to be absolutely constant, is to be considered. Atavism or reversion is the falling back to a prototype. But what is a prototype? We may take the word in a physiologic or in a systematic sense. Physiologically the signification is a [171] very narrowly restricted one; and includes only those ancestors from which a form is known to have been derived. But such evidence is of course historic. If a variety has been observed to spring from a definite species, and if the circumstances have been sufficiently ascertained not to leave the slightest doubt as to its pure origin, and if moreover all the evidence has been duly recorded, we may say that the origin of the variety is historically known. In most cases we must be content with the testimony, given somewhat later, and recorded after the new variety had the opportunity of showing its greater merits. If it now happens that such a variety of recorded origin should occasionally revert to its parent-species, we have all we can wish for, in the way of a thoroughly proved case of atavism. But such instances are very rare, as the birth of most varieties has only been very imperfectly controlled. Next to this comes the systematic relation of a variety to its species. The historic origin of the variety may be obscure, or may simply be forgotten. But the distinguishing marks are of the order described in our last lecture, either in the positive or in the negative direction, and on this ground the rarer form is considered to be a variety of the more wide-spread one. If [172] now the presumed variety sports and runs over to the presumed type, the probability of the supposed relation is evidently enhanced. But it is manifest that the explanation rests upon the results of comparative studies, and not upon direct observations of the phenomena themselves.