Part II] Hole : Regeneration of Sal (Shorea robusta) Forests 13 
interference with the passage of oxygen into the soil and by 
the activity of soil organisms accelerated by the increased moisture and 
addition of organic matter), or to the accumulation of decomposition 
products. 
(d) To further test the aeration effect of dead leaves. 
16. If the injurious action of dead leaves noted in the last experi¬ 
ment is really a bad aeration effect, we should expect it to be less opera¬ 
tive in clean sand than in the forest loam. 
In a clean sand containing lii/tle organic matter, the activity of soil 
organisms would be less with consequently less consumption of oxygen 
and production of decomposition products than in a forest loam rich in 
organic matter. In the former, also, more rapid percolation would 
allow fresh oxygen supplies to penetrate more rapidly, and decomposition 
products to be dissipated more quickly than is possible in the latter. 
A previous experiment ( Ind . For. Rec. V, 4 Part II, pp. 67-72, 1916) 
had already indicated that in such a sand a layer of dead sal leaves, 6 
leaves thick, had a beneficial rather than an injurious effect on the 
development of sal seedlings, inasmuch as it increased the soil water 
content and diminished the damage from drought. The present ex¬ 
periment was undertaken with a view to checking these results and 
those of experiment II (c) above. 
17. On August 20th, 1917, 13 pots of the same size as those used in 
the previous experiments were selected, in which a number of healthy 
sal seedlings had become established from seeds sown at the beginning 
of July 1917. These seedlings had well-developed green leaves, and had 
sent their roots well down into the soil. Six of the pots contained 
loam brought from the local Lachiwala sal forests, and the remainder 
clean river sand brought locally from the Song river, and all the pots 
were placed in full sun-fight, in the open, in the Dehra Dun Experimental 
Garden. On August 20th, 1917, a layer of dead sal leaves, 6 leaves 
thick, was placed on the surface of the soil in 3 of the loam pots and on the 
surface of the sand in 3 of the sand pots, and this layer of leaves was 
renewed on June 3rd, 1918. All the pots were lightly watered once 
daily on the days when no rain fell. The experiment was continued for 
1J years, and was closed in February 1919 when the surviving plants 
were carefully washed out of the soil and their roots measured. In the 
pots which contained a considerable number of living plants at the 
close of the experiment, several of these had become more or less 
suppressed by the more vigorous plants and the average root length, 
therefore, was obtained by measuring the roots of the 6 best plants 
in each pot. In pot 27, only 5 plants were available for measuring, 
[ 175 ] 
