360 



The Scottish Naturalist. 



indistinguishable from one another, and have proved a source of 

 much disquietude to many a botanist, who, failing to identify 

 these and other forms, has thereby taken a " scunner " at willows 

 in general. 



The causes which seem to have led the earlier salicologists 

 astray were, first, an absence of due appreciation of the excessive 

 variability of the species and of the inconstancy in characteristics 

 of the forms; and, second, ignorance of the fact that willows hybri- 

 dise with the utmost facility. Consequently, mere individual 

 conditions were placed on the same footing as true species ; and 

 not only were hybrid forms granted specific rank, but different 

 degrees of one and the same hybrid were looked upon as distinct 

 species. 



The hybridisation of willows is not mere assumption, but has 

 been proved to occur. For that matter hybridisation is now well 

 known to occur in many orders of plants ; but in willows it is 

 especially common. Not only can any willow cross with any 

 other willow, but the resulting hybrid can cross 'with any other 

 species of hybrid, and will produce fertile offspring. In this way 

 hybrids in which six species are represented can, as Wichura has 

 shown, be raised by the experimenter. In Nature, whilst hybrids 

 of two species are of common, and those of three are not of very 

 rare occurrence, more multiple hybrids have not been recognised. 

 If all species of willows occurred together and flowered at the 

 same time the number of hybrids would be legion. As it is, the 

 quantity is, perhaps fortunately, limited by circumstances of time 

 and place, but is, even then, sufficiently large. 



In the following notes on the willows of the district the species 

 will first be noticed and then the hybrids. To begin with, I may 

 say that all the British species occur in our district, and that 

 some of them are almost, though not quite, restricted — in Britain 

 —to it. 



Willows may be conveniently divided into three groups — the 

 Pleia?idrce i the Diandrce, and the Synandrce. 



I. Pleiandrae. 



Salix triandra L. Rare, and unreported from the greater part 

 of the district. I have seen it about Perth only, where it 

 appears to be native on the banks of the Tay. 



S. pentaildra L. Occurs throughout, but is local and rare. 



