GENERAL CHARACTER OF THE FLORA. 



Taking the averages, it is seen that the mean relative 

 humidity in the hot dry season is, as would be expected, least 

 in Palaman and Hazaribagh, greatest in Singbhum and the 

 Santal Parganahs. In the cold season, however, the mean 

 relative humidity becomes greatest in Palamau and Singbhum, 

 least on the plateaux. The greatest drop in mean minimum 

 temperature (vide p. 21) also takes place in Palamau, and 

 indeed (though the table does not shew this), the mean 

 relative humidity in the cold season frequently reaches 100 in 

 the early mornings, and the copious dew has a most import- 

 ant effect in keeping the herbaceous vegetation green up to 

 the end of January, and it is the season of flowering of many 

 annuals and snfEruticose perennials, esp. of Malvaceae. The 

 actual tension of aqueous vapour is much greater at Chai- 

 bassa than at Ranchi or Hazaribagh, but the statistics for 

 other stations of equal elevation are wanting. 



GENERAL CHARACTER OF THE FLORA, 



The heavy rainfall confined to a few months of the year 

 makes the climate essentially a forest one, and the province 

 still contains a considerable percentage of forest-clad land, 

 owing to the rocky nature of the surface preventing the 

 spread of cultivation. This forest belongs to the monsoon 

 type of the tropical zone, and is more or less leafless during 

 the dry season, but the cool valleys, previously alluded to 

 (p. 7), contain a flora which somewhat differs from the 

 general type, and the tops of some of the highest hills, parti- 

 cularly Parasnath, possess species of a moister climate. 

 Although essentially tropophilous, there is yet a marked 

 tendency towards xerophilous structure, which is seen, e.g., 

 in the most characteristic tree of the area, the Sal. In the 

 Sal tree the leaves 1 are very nearly persistent, and they thus 



x The Tipper surface has a thick cuticle and large epidermal cells rather 

 deeper than broad. Beneath this are 2-3 rows oi thin-walled palisade 

 cells. This tissue is interrupted at frequent intervals by large thick - 

 walied sap tissue opposite the vascular bundles and, with the numerous 

 bast fibres of these bundles and a similar tissue opposite to the bundle 

 interrupting the spongey parenchyma, forms strong supporting strands 

 which render the leaves very firm. 



