DISTRIBUTION OF PLANTS. 



429 



Of two Boreal, or European forms found in sub-tropical countries, 

 that form is the most northern which flowers, etc. in the coldest 

 season, hence Veronica and Ranunculus are more northern than 

 Epilobium in this particular district. The most elevational plant at 

 Cabul is Cardaminoidea, floribus luteis, this flowers at high altitudes 

 in August and September, and at Cabul shows no symptom of flower- 

 ing even in October ; it is there a winter plant ? The same is true of 

 Hippuris, which to flower at Cabul requires a greater degree of cold 

 than is obtainable during the summer months. 



What I have said of Epilobium above, is true of Typha and Arundo, 

 both now passed flowering, and both found in India, to a considerable 

 extent. 



Royle's idea of the comparatively greater extent of distribution of 

 water plants is not I think correct, in the sense he seems to entertain 

 it ; to be so, the species should be the same, which they are certainly 

 not. It is only with pre-eminently aquatic forms that the annual 

 temperature can be more equalised than obtains with strictly terres* 

 trial plants. The humidity which may appear connected with the 

 rapid evoporation in these countries, and which obtains ? in the vici- 

 nity of all bodies of water, may account for the appearance here of 

 Arundo, etc. All genuine aquatic types have leaves involute in 

 vernation ? 



The least valuable of all northern forms, are those associated with 

 cultivation, especially if they be annuals, because in the first place they 

 may be acclimated species, a circumstance of great importance ; and 

 in the second, because if annual, they are confined to the cold season. 

 All such forms have probably migrated into these countries, they 

 have come from the westward : this shows us why at almost equal 

 elevations they are most common, the nearer we approach to the ele- 

 vated regions towards the west, because it is self-evident that the 

 nearer we approach the regions whence they have migrated, the 

 more abundant and diversified will the migrating plants be, only 

 particular species having the power of extending the range of migra- 

 tion. 



When all the Indian plants hitherto met with, have been tabulated ; 

 when all their respective heights at which they have been found have 

 been determined ; when their more strictly geographical sites have 

 been fixed ; when we have some data as to the quantity of humidity 

 pervading their localities ; then, and not till then, shall we be able to 

 legislate for the geography of Indian botany. 



