BOTANICAL GEOGRAPHY. 



397 



The polarity of Grasses, Saxifrageae, and Moses, is greatest in res- 

 pect to numbers, and next to these are Cruciferae, Ranunculaceae, 

 and Caryophyllese. 



It is precisely these orders that are most indicative of elevation, 

 and of these, Grasses of northern forms, and Saxifrageae, are those 

 to obtain which in low latitudes, one must ascend very high ; excep- 

 tions of course occur, but in such cases we must not look exclusively 

 into details. 



So far as grasses are concerned, the number of northern forms in 

 India appears small, we must except of course many of the northern 

 Cerealias, which may be supposed to have been acclimated. Barley, 

 oats, and wheat, with one or two others, are therefore tlie exceptions. 



So far as my own observations, go, nine out of ten grasses, even to 

 an elevation of 9000 ft. are tropical, and belong almost exclusively 

 to Andropogonese. 



In the Khasya mountains, grasses form a predominant feature, 

 yet I only know of a very few insta'.ices of northern forms 



In Bootan the same is the case, although grasses form a much less 

 predominant feature than on the before mentioned mountains ; the 

 most common species is the lemon grass. 



The detection of the fruit of a Leguminous plant, probably 

 of the sub order Mimose«, by Mr. McClelland or the Khasyah 

 Mountains between Surareem and Churra, and at an elevation of 

 about 5000 ft., would lead me to infer (if an inference may be 

 drawn from a solitary instance), that during the period of the exis- 

 tence of the fragment alluded to, the laws regulating the distribu- 

 tion of vegetables, were in the tropics, much the same as they are 

 now. Taking the site of the raised fossil marine Beach, p, 171, as 

 the sei line at th;it period, the height of the mountains would be 

 minus the present elevation of the sea beach ; in other words, the 

 elevation at wh;ch the plant flourished, was about 300O ft., instead 

 of oOOO. 



This corresponds well with our vegetation as it now exists ; since 

 the elevational limits of such plants, may be stated with tolerable 

 confidence to be 3000 ft. 



It is perhaps not unworthy of remark that a prickly Mimosea now 

 exists on the fossil Sea beech itself, the conformation of its fruit 

 however is materially different from that of the fossil. 



