108 TRANSACTIONS OF THE [Sess. lxxxi 



Chinese annuals, witli none of which >S. Praegerianum has 

 any affinity. But a closer parallel among species which, 

 being in cultivation, are fully available for comparison, is 

 found in S. jyrimuloides, Franchet, one of Delavay's 

 Yunnan plants, now well known in gardens (Plate III, 

 fig. 4). In S jjrimuloides similar rosettes of entire stalked 

 leaves (in this case ovate, fig. 6) are found, but in 

 *S^. primuloides the root-stock is slenderer, much-branched, 

 and aerial, forming a tiny bush, each branch with a 

 terminal leaf-rosette. Next, the axillary flower-stems of 

 aS^. Praer/erianuvi are most unusual in the genus, but are 

 again exactly matched in S. pri mil do ides, which agrees 

 further in its ovoid flowers (fig. 5) ; this last feature, also 

 very unusual in Sedum, is on the other hand approached 

 in a few of the Rhodiolas — for instance, in 8. rariflorum, 

 N. E. Br., a recently described Chinese species (fig. 7). 

 So that the affinities of ;Sf. Praegerianum appear to lie 

 with the Rhodiola section on the one hand, and more 

 directly with S. 'primidoides on the other. 



An examination of *S^. Praegeria,nu7)i reveals another 

 feature unusual in Sedum. The petiole widens at the base 

 to three or four times its normal diameter (fig. 3), and is 

 attached to the root-stock by the whole breadth of this 

 expansion, so that the cicatrix produced by removing a leaf 

 is a horizontal line running round a considerable arc of the 

 periphery of the root-stock. To find an analogue to this, 

 we turn again to *S'. priimdoides, where a precisely similar 

 form of leaf-base is found (fig. G). It seems clear, then, 

 that there is a close aflinity between 8. Praegerianum and 

 S. 'primuloides ; but where are these two aberrant species 

 to be placed in a classification of the genus ? 



The points of i-esernblance between aS^. Praegerianum^ and 

 the Rhodiola section of Sedum have been pointed out 

 already. Rhodiola, as established as a genus by Linnaeus 

 (Genera Plantarum, ed. i, p. 318, 1737), envisaged only 

 those plants, now usually placed under Sedum, which have 

 dioecious, tetramerous flowers. Scopoli (Introd. ad Hist. 

 Nat., 255, 1777) employed the term in the same sense, 

 as a section of Sedum. As knowledge of these plants 

 increased, it became clear that in a hard-and-fast sense 

 this definition could not stand, as closely allied plants 



