xii FLORA OF MADRAS. 



Impatiens, to which Sir Joseph attributed about 50 species, whereas 

 the present work includes 81. 



It is interesting to compare the ten dominant families with 

 similar lists drawn up by Sir Joseph Hooker, as follows : 



Position in list for 



Geraniaceae with 92 species (including Balsaminaceae) comes 

 close to Asclepiadaceae, and is likely to outstrip it in the future. 



The number of Dicotyledons is slightly more than three times 

 that of Monocotyledons, and there are only 5 indigenous Gymno- 

 sperms. 



In spite of, perhaps because of, its numerous components it is 

 difficult to split up the area into very well-defined regions, and still 

 more to fix clear limits to them, although the typical characteristics 

 of each are susceptible of differentiation. There is so much over- 

 lapping, intrusion and shading off from one to the next that only 

 a minutely detailed description of each can give a clear idea ; an 

 ecological study would involve the compilation of several volumes. 

 Much the same would apply to the variations within each region 

 due to the influence of elevation, atmospheric, topographic and 

 phreatic moisture and to changes in soil. On the hills the flora 

 peculiar to the higher slopes and plateaux may intrude into a lower 

 and dryer region along the streams, and the more xerophytic species 

 often climb upwards along exposed and eroded spurs. Unfor- 

 tunately, detailed ecological investigation is lacking. The examina- 

 tion, in more or less detail, of one range of hills has shown that 



