The law of reversion is equally powerful with hybrids, when they are sufficiently fertile to breed together, or when they are repeatedly crossed with either pure parent-form, as with mongrels. It is not necessary to give instances, for in the case of plants almost every one who has worked on this subject from the time of Koelreuter to the present day has insisted on this tendency. Gaertner has recorded some good instances; but no one has given more striking cases than Naudin.[83] The tendency differs in degree or strength in different groups, and partly depends, as we shall presently see, on the fact of the parent-plants having been long cultivated. Although the tendency to reversion is extremely general with nearly all mongrels and hybrids, it cannot be considered as invariably characteristic of them; there is, also, reason to believe that it may be mastered by long-continued selection; but these subjects will more properly be discussed in a future chapter on Crossing. From what we see of the power and scope of reversion, both in pure races and when varieties or species are crossed, we may infer that characters of almost every kind are capable of reappearance after having been lost for a great length of time. But it does not follow from this that in each particular case certain characters will reappear: for instance, this will not occur when a race is crossed with another endowed with prepotency of transmission. In some few cases the power of reversion wholly fails, without our being able to assign any cause for the failure: thus it has been stated that in a French family in which 85 out of above 600 members, during six generations, had been subject to night-blindness, "there has not been a single example of this affection in the children of parents who were themselves free from it."[84] * * * * * _Reversion through Bud-propagation--Partial Reversion, by segments in the same flower or fruit, or in different parts of the {37} body in the same individual animal._--In the eleventh chapter, many cases of reversion by buds, independently of seminal generation, were given--as when a leaf-bud on a variegated, curled, or laciniated variety suddenly reassumes its proper character; or as when a Provence-rose appears on a moss-rose, or a peach on a nectarine-tree. In some of these cases only half the flower or fruit, or a smaller segment, or mere stripes, reassumed their former character; and here we have with buds reversion by segments. Vilmorin[85] has also recorded several cases with plants derived from seed, of flowers reverting by stripes or blotches to their primitive colours: he states that in all such cases a white or pale-coloured variety must first be formed, and, when this is propagated for a length of time by seed, striped seedlings occasionally make their appearance; and these can afterwards by care be multiplied by seed.