l6 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



of these, such as ab' c, a b' c', a' b' c, a' b c, and so on. The best- 

 marked variant from the type abc would be a' b' c', and even such 

 a form as a b' c' might be allowed varietal rank were it not for the 

 existence of the forms ab' c and a b c'. To this must be added the fact 

 that a, b, c, a', b', and c' are not constant quantities, but exist in inter- 

 mediate degrees which connect a and a', and so on. Thus, glaucescence 

 may vary by imperceptible degrees into green, and an ovate leaf 

 into a lanceolate or linear leaf. So that in diagnosis we have to deal not 

 only with the number of characters in which a form may agree with 

 or approach a well-marked variety, but with the degree in which 

 each of these characters is present. To conclude, the study of a large 

 growing series of forms of the variable species of Sedum as found in 

 cultivation puts one out of conceit with the application of varietal 

 names to most of them. 



But it may be pointed out that, owing to the absence of inter- 

 mediates in a given area, such forms may assume a very definite local 

 importance, which may fully justify their being dealt with in local 

 floras, though on a wider view their distinctness may disappear. It 

 may be added that the study of a large series of Sedums derived from 

 garden sources has this bearing on the botanical as opposed to the 

 horticultural side of the question : that as Sedums are almost invari- 

 ably propagated by division, and as they do not tend in most cases 

 to seed themselves in gardens, the numerous garden forms un- 

 doubtedly mostly represent wild forms, and give a true conspectus 

 of the natural range of variation of the different species. 



VI. Cultivation and Propagation. 



Most Sedums are of the easiest cultivation, and given perfect 

 drainage and a light soil no difficulty will be experienced. Many — 

 though not all — are especially at home on an old wall, where they 

 will withstand any degree of drought. The vitality as against want 

 of water of many Sedums is indeed remarkable, and few plants are 

 better fitted to endure the adverse conditions of soil and moisture 

 which are found, say, on a wall-top. But it would be a mistake to 

 imagine that such conditions are necessary or favourable to their 

 growth. The majority flourish best under ordinary garden treatment ; 

 some, such as the Telephiums, prefer a rich moist soil ; and one or 

 two, such as the European S. villosutn and the North American 

 S. pulchellum, though possessing a succulence as great as many of 

 the most xerophilous species, actually require in many gardens marshy 

 conditions to secure their continuance. 



The majority of the Sedums found in cultivation are quite hardy 

 in our cHmate, but a considerable minority cannot be so classed. 

 Thus, the Mexican Sedums come from a tolerably warm cUmate, 

 and as a whole are best suited to a cool house. Their hardiness in 

 the British climate has not as yet been fully tested save in a few 



