XXIII. Upon the differgnt Species of esculent Strawberries. By 
Thomas Andrew Knight, Esq. F.R.S. 4 L.S. Pres. Hort. Soc. 
Read May 6, 1817. 
Bsrore 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 inter- 
mix, 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 there- 
fore disposed to question the specific difference of the Amygdalus 
communis and 4. 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 
Iam much disposed to question the claims of many of the it inter- 
mediate supposed species to their present titles. - 
Many plants of the following species and varieties of straw- 
berries 
