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XXIII. Upon the different Species of esculent Strazcherries. Bij 

 T/iomas Andrew Knight, Esq. F.R.S. <5- L.S. Pres. Hort. Soc. 



Read Mai/ 6, 1817. 



Before 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 

 ine to be often used somewhat vaguely and licentiously by writers 

 iipon 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 ni^' 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 

 coynmunis 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' Rtisseltiana, and the pollen of the S.alba; and therefore 

 I am much disposed to question the claims of many of the inter- 

 mediate supposed species to their present titles. 



Many plants of the following species and varieties of straw- 

 berries 



