1916-17.] BOTANICAL SOCIETY OF EDINBURGH 



157 



Rhododendrons of the Irroratum Series. 

 Professor Bayley Balfour, F.R.S. 



(Read 8th February 1917.) 



By 



The series of Rhododendrons which we may call Irroratum, 

 after the first described species included in it, has a wide 

 area of distribution in Yunnan, and to our present know- 

 ledge extends only into Eastern Upper Burma over the 

 Yunnan frontier. Its extreme limits in Yunnan as known 

 are Mengtsz in the south-east, Tengyueh in the west, Tseku 

 in the west-north-west, and the Chungtien plateau in the 

 east-north-west. Fourteen species of the series are known. 

 The following list gives their names, the distribution of each, 

 and the name of its discoverer : — 



Rh. adenostemonum, 



Balf. f. eL W. W. Sm. 

 Rh. agastum, Balf. f. et 



W. W. Sin. 

 Rh. anthosphaerwm, 



Diels. 

 Rh. araiophyllum,^a.U. 



f. etW. W. Sm. 



Rh. ceraceum, Balf. f. 



et W. W. Sm. 

 Rh. eritiTnum, Balf. f. 



et W. W. Sm. 

 Rh.gymnanihum, Diels. 



Rh. hylothreptum, Balf. 

 f et W W. Sm 



Rh. irroratum, Francli. 



Rh. lukiangense, Francli. 

 Rh. mengtszense, Balf. f. 



et W 'W. Sm. 

 Rh. pogonostylam,, Balf. 



f. et \V. W. Sm. 

 Rh. spanotrichum^ Balf. 



f. et W. W. Sm. 



Rh. tanastylum, Balf. f. 

 et Ward. 



S.E. Yunnan. 

 W. Yunnan. 

 E.N.W. Yunnan. 

 W. Yunnan. 



W.N.W. Yunnan. 



E.N.W. Yunnan. 



W.N.W. Yunnan. 



E.N.W. Yunnan. 



Mid. N.W. and 

 E.N W.Yunnan 



W.N W. Yunnan. 

 S.E. Yunnan. 



S.E. Yunnan. 



S.E. Yunnan. 



E. Upper Burma. 



N. of Mengtsz. 8500 ft. 

 (Henry.) 



Sliweli - Salween divide. 

 7000-9000 ft. (Forrest.) 



Sungkwei pass. 10,000- 

 11,000 ft. (Forrest.) 



Shweli - Sahveen divide. 

 9000-10,000 ft. (For- 

 rest.) 



Tseku. (Monbejg.) 



Clumgtien plateau. 9000 

 ft. (Forrest.) 



Tseku. 13,000 ft. (For- 

 rest.) 



Sungkwei pass. 11,000- 

 12,000 ft. (Forrest.) 



Tali range to the Chung- 

 tien jjlS't^eau. 9000- 

 12,000 ft. (Delavay.) 



Tseku. (Soiilie.) 



S.E. of Mengtsz. 7000 ft. 

 (Henry.) 



N. of Mengtsz. 7000- 

 8500 ft. (Henry.) 



Fengchenlin Mts., S.W. 

 of Mengtsz. 7500 ft. 

 (H.nry.) 



Hpimaw. 9000 - 10,000 

 ft. (Ward.) 



Two of these species are in cultivation — Rh. hylothreptum 

 and Rh. irroratum. A third plant belonging to the series 



