I must not conclude without suggesting a hypothesis about the two kinds of cherry. They differ but little in character, and, what is very rare, their two ancient habitations, which are most clearly proved, are similar (from the Caspian Sea to Western Anatolia). The two species have spread towards the West, but unequally. That which is commonest in its original home and the stronger of the two (_P. avium_) has extended further and at an earlier epoch, and has become better naturalized _P. cerasus_ is, therefore, perhaps derived from the other in prehistoric times. I come thus, by a different road, to an idea suggested by Caruel;[1041] only, instead of saying that it would perhaps be better to unite them now in one species, I consider them actually distinct, and content myself with supposing a descent, which for the rest it would not be easy to prove. +Cultivated Plums.+ Pliny[1042] speaks of the immense quantity of plums known in his time: _ingens turba prunorum_. Horticulturists now number more than three hundred. Some botanists have tried to attribute these to distinct wild species, but they have not always agreed, and judging from the specific names especially they seem to have had very different ideas. This diversity is on two heads; first as to the descent of a given cultivated variety, and secondly as to the distinction of the wild forms into species or varieties. I do not pretend to classify the innumerable cultivated forms, and I think that labour useless when dealing with the question of geographical origin, for the differences lie principally in the shape, size, colour, and taste of the fruit, in characters, that is to say, which it has been the interest of horticulturists to cultivate when they occur, and even to create as far as it was in their power to do so. It is better to insist upon the distinction of the forms observed in a wild state, especially upon those from which man derives no advantage, and which have probably remained as they were before the existence of gardens. It is probably only for about thirty years that botanists have given really comparative characters for the three species or varieties which exist in nature.[1043] They may be summed up as follows:— _Prunus domestica_, Linnæus. Tree or tall shrub, without thorns; young branches glabrous; flowers appearing with the leaves, their peduncles usually downy; fruit pendulous, ovoid and of a sweet flavour. _Prunus insititia_, Linnæus. Tree or tall shrub, without thorns; young shoots covered with a velvet down; flowers appearing with the leaves, with peduncles covered with a fine down, or glabrous; fruit pendulous, round or slightly elliptical, of a sweet flavour. _Prunus spinosa,_ Linnæus. A thorny shrub, with branches spreading out at right angles; young shoots downy; flowers appearing before the leaves; pedicles glabrous; fruit upright, round, and very sour.