Page:Transactions of the Linnean Society of London, Volume 12.djvu/426

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I enter upon the immediate subject of the following communication, it will be necessary that I define precisely the meaning which I annex to the word species; as that appears to me to be often used somewhat vaguely and licentiously by writers upon botanical subjects. By a species of plants, I mean all plants which can be made to breed together without producing mules; that is, without producing plants which are incapable of affording offspring by seeds: and I consider all plants to be of distinct and different species which cannot be made to breed with each other (if capable of breeding at all), or which, if they intermix, produce mule plants. The peach and nectarine tree have, under my care, bred very freely with the bitter-almond tree; and the offspring do not appear to be mule plants: and I am therefore disposed to question the specific difference of the Amygdalus communis and A. persica. Similar experiments have led me to doubt the specific difference of the cultivated plum and sloe; and I possess several varieties of the willow, which are not mules, and which appear to have derived their existence from seeds of the Salix Russelliana, and the pollen of the S.alba; and therefore I am much disposed to question the claims of many of the intermediate supposed species to their present titles.

Many plants of the following species and varieties of berries