TRANSACTIONS 



BOTANICAL SOCIETY OF EDINBURGH. 



SESSION LXXX. 



Some Plant Associations of N.W. Yunnan. 

 By F. KiNGDON Ward, B.A., F.R.G.S. 



(Read lOtli February 1916.) 



Examination of the flora of any region shows that the 

 plant formations fall naturally into two main groups : the 

 tirst dependent on tlie general climate of the region as 

 determined by its latitude and surrounding physiographieal 

 features, the climate being described as arctic, continental, 

 temperate, maritime, monsoon, equatorial, desert, and so on ; 

 the second determined by local and varying conditions, 

 such as shelter, altitude, rate of change of temperature, or 

 water — factors which modify and in extreme cases mask 

 the regional climate and its efl:ects, while difterences of soil 

 introduce a selective element, altering, with the aid of 

 mechanical causes, the plant associations. To the former 

 may be given the name of dominant forinations, while the 

 latter, which are in the nature of the case numerous in any 

 given region, may be distinguished as incidental forma- 

 tions, or associations. It will, however, be readily recognised, 

 if this distinction is made, that the terms are relative. 

 A formation such as forest may be dominant in one region — 

 for instance, round the equatorial belt and over a large part 

 of the monsoon area — and incidental in another, as where 

 it fringes a watercourse in arid country ; and in Europe 

 the original dominant formations, if temperate — as opposed 

 to coniferous — forest, or grassland (meadow), have often 

 been so much interfered wath hy man as to be obscured. 



TEANS. BOT. SOC. EDIX. VOL. XXVn. 1 



