1916-17.] BOTANICAL SOCIETY OF EDINBURGH 117 



Group 2. Brevicaules. — Root-stock very short, branched 

 slightly or not at all. 



Balfouri, R. Haniet. Levii, R. Hamet. 



Durisi, R. Hamet. 'iMosdi, R. Hamet.^ 



Hobsonii, R. Hamet. * Praegerianum, W. W. Sm. 

 Karpelesae, R. Hamet. 



According to the views brought forward above, the oldest 

 type of Rhodiola now living is represented by S. Praegeri- 

 anum, with short caudex and large caudex-leaves. Thence 

 a complicated series of forms shows a progressive increase 

 in length and thickness of caudex and decrease in size of 

 the caudex-leaves ; ;S^. prhnuloides, S. Levii, S. Smithi, for 

 instance, being progressive steps to the crassipes type, 

 where the caudex-leaves, now reduced to mere scales at the 

 summit of aerial succulent root-stocks, still show when 

 young a green, leaf-like colour and a tendency to an in- 

 cipient (or rather relict) lamina. At this point in the 

 series the flowers, hitherto perfect and pentamerous, begin 

 to show a tendency to dioecisrti and tetramerism, which 

 becomes more pronounced as caudex development increases 

 and scale development weakens, till in aS'. roseum and its 

 allies we have a group of species with massive caudices 

 crowned with small chafly scales, from the axils of which 

 rise strong stems bearing corymbs of dioecious tetramerous 

 flowers. It is important to note that seedlings throughout 

 the whole series, from Praegerianwni to roseum (so far as 

 I have had an opportunity of studying them), show what is 

 here taken to be the primitive type of caudex-leaf — a leaf 

 having a lanceolate to orbicular lamina, and a petiole with 

 a broad clasping base. The different types of leaves found 

 still persisting among the primitive Prhnuloides series can 

 be matched, often with a remarkable closeness, in the seed- 

 ling stage of members of the Crassipedes, Himalenses, and 

 Roseae, the mature plants of which bear only scales. 



As regards the question of the geographical distribution 

 of the plants dealt with above, the Rhodiolas are essentially 

 an Asiatic group. One species only (the N. American 

 S. rhodanthum, A. Gray) does not occur in Asia ; and only 

 one other {S. roseum, Scop.), which is also the most variable 



^ Caudex missing in the type specimens. Appears to be allied to 

 S. Balfouri. 



