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water in a lake, and the height to which it rises is 

 usually clearly marked by a definite line above 

 which growth is uninjured. This was well seen in 

 the Sal forests of the Dehra Dun during the 

 severe winter of 1904-05, a definite line being clearly 

 visible, running along the flanks of the Siwaliks, 

 below which the leaves on every tree were brown 

 and dead, those above the line being green and 

 uninjured. The presence of large quanti- 

 ties of water in the soil may considerably reduce 

 the air temperature, as may also a heavy growth 

 of grass which reduces the temperature by 

 radiating heat, transpiring moisture, interfering 

 with the free circulation of air, and with the access 

 of heat to the soil. Observations have shown 

 that the temperature on an area covered with 

 grass may be 16 F. lower than that of a similar 

 area with no vegetation. The effect of frost 

 depends of course largely on the condition of the 

 plant itself. Consequently two trees of the same 

 species may be very differently affected in different 

 localities. One growing in a damp warm valley 

 may be killed, while another, in a more exposed 

 situation at a higher elevation, may escape injury ; 

 the former owing its susceptibility chiefly to the 

 longer period of its vegetative activity, the larger 

 quantity of water in its tissues and to the latter 

 being less completely lignified or otherwise matured. 

 (2) The indirect drying up and killing of plants or parts of 

 them, the injury being caused in precisely the same 

 manner as in the case of drought. When the soil 

 temperature falls below a certain point the root 

 hairs are no longer able to absorb the necessary 

 supplies of water. While the roots are thus inactive, 

 the leaves may be actively transpiring moisture 

 under the influence of bright sun-light and dry air- 

 currents. The leaves and branches may thus become 

 completely dried up and killed. Trees which retain 

 their leaves in winter are particularly liable to this 

 form of damage and mahua (Bassia latifolia) and 

 achar (Buchanania latifolia) may frequently be seen 

 injured in this way. This mode of injury may often 

 be recognised by the leaves commencing to die 

 back from the tip, the tissues at the base of the 



