Part II] Hole: Regeneration of Sal (Shorea robusta) Forests * 59 
(10) In a sal seedling the most resistant portion of the plant, which 
retains vitality longest under unfavourable conditions, 
is the collum. This includes the insertions of the cotyledons, 
from the axils of which new shoots develop to replace those 
which die back. It is remarkable that, in sal seedlings, 
an internode often of considerable length separates the 
insertions of the two cotyledons, see l.c. part I, 1914, para. 
16, p. 30 (footnote), para. 30 (6). 
(11) Drought, if sufficiently severe, suffices to kill the strongest 
plants. Drought of less severity, however, only kills the 
weakly plants and causes the so-called 4 4 dying back ” of 
the more vigorous individuals, see l.c., part 1,1914, para. 16. 
(12) In pot cultures, whereas 70—100 per cent, of the seedlings 
which are watered remain healthy and do not die back, 100 
per cent, of those which are not watered do die or die back. 
This emphasizes the importance of drought as the factor 
responsible for death and dying back, see l.c. part I, 1914, 
para. 12 (2). 
(13) This is further emphasized by the fact that sal seedlings grown 
in the open in the Dehra Dun Experimental Garden, where 
the soil is kept moist by periodic sub-soil irrigation, develop 
vigorously from the first and do not die back. Such plants 
show, already in their second year, the swollen 44 carroty ” 
stem characteristic of vigorously growing plants and produce 
an almost constant average annual height growth of 32 
inches between the ages of 2 and 8 years, the most vigorous 
plants attaining a height of 29 feet at the age of 8J years, 
see l.c. part II, 1916, p. 44 and Plate II, also the present 
paper, para. 6 and Plate I. 
(14) During the period October-May in the local sal forests, the 
seedlings are found to die or die back chiefly in those months 
when the least rainfall is received. During this period, 
also, the moisture content of the upper soil layers frequently 
attains the death limit during spells of dry weather. The 
deaths and dying back in the local forests during these 
months, therefore, is believed to be due chiefly to drought,* 
see l.c. part II, 1916, paras. 18, 19. 
(15) Pot cultures have shown that, while it is practically impossible 
to give too much water to sal seedlings growing in well- 
* In large clearings and open grasslands in the locality, seedlings are commonly cut 
back by frost in the cold season Novembcr-February, but apart from altogether excep¬ 
tional seasons, such as the cold weather of 1904-05, frost does very little damage in 
the sal forests themselves. 
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