161 DIOECIA— DIANDRIA. Sallx. 



If different circumstances may prevent, or promote, the 

 production o^Jio-doers at all, see Intr. to Botany, ed. 5. 113, 

 they may siu'ely cause the above alteration ; which though 

 diflerent, is not more surprising than peaches and nec- 

 tarines, varying every year in comparative quantities, 

 along with some individual fruits, half peach, half necta- 

 rine, which I have seen and tasted, from the same tree. ^ 



The arrangement of the species of Willows is a matter of 

 considerable difficulty, as well as their technical discri- 

 mination. The smoothness or hairiness of their leaves, 

 is in many cases variable, and when decided, or constant, 

 often widely separates species naturally allied. The 

 margin of those parts, whether entire, serrated, crenate, 

 or toothed, cannot in all cases afford an indisputable 

 character. The stipulas are variable in many respects. 

 A suggestion in Fl. Br, 1072, recommending \\\e germen, 

 whether sessile or stalked, the length of the style, and the 

 division of the stigmas, for discriminating natural sec- 

 tions of the genus, met with the approbation of some good 

 botanists, and has been adopted by Wahlenberg, with 

 the addition of the germen being downy or smooth ; but 

 the characters thus obtained, though excellent for the 

 discrimination of species, do not lead to their natural ar- 

 rangement. No good plan having yet been proposed, I 

 have in Rees's Ci/clopcedia, and pretty nearly in the pre- 

 sent work, followed that of Willdenow, which is liable to 

 as few exceptions as any other. It is always advisable, 

 in such undertakings, to be led by common usage, rather 

 than doubtful speculation, and especially to avoid altera- 

 tion, for the sake of alteration alone. 



In the far more arduous undertaking of specific definition, 

 the most able critics will be the most aware of my diffi- 

 culties. Full 30 years have I laboured at this task, 10 

 of them under the instructive auspices of my late friend 

 Mr, Crowe, in whose garden every Willow that could be 

 got was cultivated; more especially all that could be ob- 

 tained from any part of Britain, by that unrivalled col- 

 lector Mr. Dickson. The plants were almost daily vi- 

 sited and watched by their possessor, whom no character 

 or variation escaped ; seedlings innumerable, springing 

 up all over the ground, were never desti'oyed till their 

 species were determined, and the immutability of each 

 verified by our joint inspection. This was the more ma- 

 terial, to set aside the gratuitous suppositions of the mix- 



