Introduction. : 3 
thus both greatly increasing general growth and 
fostering its vigour. 
It is true that under any circumstances the sun 
heats the surface of the soil ; yet, even in the hottest 
weather, this direct influence of the solar rays 
descends only a few inches into the ground, and 
can do little to neutralise the chilling effects of 
evaporation and a water-logged condition. Further, 
in ill-drained land, this superficial heating, in con- 
junction with the wetness of the soil, speedily leads 
to the formation of a baked surface, very impervious 
to moisture; so that any rain which falls upon it, 
instead of sinking in, immediately- runs over the 
surface, dissolving any soluble matter lying upon it, 
and discharging it into the nearest hole, or carrying 
it away on to any adjacent walk. 
Hence, in the absence of efficient drainage, rain is 
actually injurious rather than beneficial to the land, 
even while it is indispensable. When, on the other 
hand, the rain can penetrate where it falls, it carries 
down ‘to the roots of the plants whatever it dissolves 
in its course, and thus promotes growth. 
Further, by again distributing throughout the 
whole body of the soil such saline matters as the 
constant action of evaporation would otherwise with- 
draw from the general mass and accumulate on or 
near the surface, it helps to preserve the average 
constitution of the bulk of material from steady 
impoverishment, and removes the danger of total 
loss of any of its constituents through exposure. 
Again, if the drainage is good, no substances 
which are injurious to the roots of the plants can 
B2 
