208 
Records of Ike Geological Survey of India, 
[vot. xtir. 
tlirougli tlie moisture in tlie soil. Lastly, plants also induce capillary currents 
towards themselves. The absorbing parts are the rootlets and myriads of hairs 
surrounding each. These, by the act of absorption, set up capillary currents in 
the moisture of the soil towards themselves, which compete with capillary eva¬ 
poration at the surface and tend to the diffusion of the moisture and its salts 
tlu’ougb the soil as far as the roots extend. It is to be noted that if a soil re¬ 
main damp, so that the salts arc diffused through it, they may do no harm. It 
is their concentration as a scum on the surface that poisons crops. The moisture 
round the rootlets forms a solution so saline that the osmose currents by which 
the plants are nourished are interfered with and they perish. 
27. A very important point materially affecting the question of the cure 
of reh, is how far reclamation or non-development may bo duo to diffusion 
of the salt in the soil. In rainy and damp portions of the plains similar in 
conditions of subsoil drainage to reh-stricken tracts, we find no efflorescence. 
How far is this due to surface washing and how far to diffu.sion ? From three 
experiments made this year, it was found that the rain waters coming off tho 
surface of reh-ground contained a perceptible quantity of the salts. Neverthe¬ 
less the great fact of occlusion by means of tho first soakage portion of the 
rainfall was proved by the occurrence of a copious efflorescence on the drying 
of the washed soil. If the rainfall were very copious, would it succeed in wash¬ 
ing off excess of salt ? This question might be settled by analysis of the total 
quantities of sohrblo salt in soils of the rainy and dry tracts of the plains, 
within the range of surface soakage. As it would be impossible to select two 
spots precisely similar in conditions of subsoil drainage and constitution of soil, 
it is evident that no conclusion would bo of value except from a great number of 
experiments. 
28. Speaking broadly, tho development of efflorescences occurs in India 
chiefly in a well-marked meteorological area, including the Punjab, except at the 
base of the hills, similarly the upper part of tho North-Western Provinces, 
and also Sinde and Rajputana. This region is characterised by small rainfall, 
dryness of the air, and excessive solar heat, each of these as shown contribute 
to the concentration of salt on tho surface. On tho other hand, in similar 
jiarts of the Indo-Gangetic plain, where there is more copious rainfall, this of 
itself by keeping tho soil moister causes diffusion of any salt present through 
tho soil. Again, the sheet of air which covers the ground contains more 
moisture and acts in two ways in preventing surface concentration. It dimi¬ 
nishes tho effect of solar heat, because, as Tyndall has shown, the invisible 
vapour of -water absorbs a groat deal of tho heat, thus preventing damp regions, 
such as Lower Bengal, from reaching such high temperatures as the dry regions 
of Upper India, even though tho latter are of higher latitude. In addition, there 
is more cloud in the damp regions which also abstracts solar radiation, whereas 
in Upper India the sky is cloudless most of the year. Again, the presence of a 
moister sheet of air over the ground abstracts evaporation, which takes jjlaco 
in proportion to the dryness of the air. It is very desirable that a series of 
experiments should be made regarding tho total salts occluded in the drier and 
moister parts of the plains within the ranges of surface soakage and evaporation. 
