Pakt II] Hole : Regeneration of Sal (Shorea robusta) Forests 23 
per square foot of area*. The present experiment has shown 
that the result of one complete sowing is 30 such plants in 
54 square feet, which gives a ratio of 0-6 plant per square 
foot or about half the total number required. Thus, even 
under the very exceptional conditions of an unusually favour¬ 
able season for germination and early growth, with the seeds 
buried in the surface soil and not sown broadcast, and with 
the soil thoroughly dug and free of raw humus, it would 
apparently require at least two exceptionally good seed years 
to give a full stock of seedlings. The combination of an 
unusually favourable season with an exceptionally good seed 
year would be very rarely attained, and there is no doubt 
that the above figures are far too favourable for us to base 
upon them an estimate of the probable average results to be 
expected from natural regeneration. It will be noted that 
in Plot Y, of the plants existing at the end of the 2nd year 
only about \ survived to attain 10 inches in height at the 
end of the 5th year (34 per cent, survivors in 1915 and 8 per 
cent, survivors in 1919), hence we ought to aim at getting 4 
plants per square foot at the end of the second year, if we 
wish ultimately to obtain 1 plant, 10 inches high, per square 
foot. 
In experiments VI, VII and VIII below, it is shown that, on an 
average of three years’ work in 1916-1918, one heavy broad¬ 
cast sowing in the shade, on soil which has been dug after 
being freed of dead leaves, results in only 0-1 plant per 
square foot of area surviving after 1 to 1^ years. Thus 40 
such sowings would be required to produce a full stock of 
seedlings (4 plants per square foot) and the period required 
to obtain these, therefore, is 40 years. As this calculation 
of 40 years has been based on the favourable conditions of 
a dug soil free of dead leaves, and a full supply of seed 
annually, it is believed that it may be safely accepted as 
the minimum period permissible. 
After 40 years, then, we may expect a sufficient stock of seed¬ 
lings on the ground, the average age of which will be 20 years 
with an average height of 30 inches. 
* If the development of a full crop of young sal seedlings is watched, it is usually found 
that the plants which survive and are most vigorous at any particular stage of growth, 
at any rate up to a height of 3-4 feet, are separated from one another by an average 
distance roughly equal to their height. 
[ 185 ] 
