170 Forestry Quarterly 



Evaporation from Tops 



Per Cent of 

 Exposure Fresh Weight Lost 



8 min. 0.62 



21 " 1.46 



35 " 2.50 



49 " 3.10 



65 " 3.75 



82 " 4.8 



109 " 5.8 



150 " 7.0 



40 hrs. 46.0 



70 " 54.0 



100 " 59.0 



220 " 61.0 



In another connection some interesting figures developed from 

 loss of weight of the white root tips. The data given below are 

 not a fair figure for comparison, but are suggestive nevertheless. 

 Long white roots grown in water from a willow cutting were 

 weighed at intervals of about 10 minutes, between weighing they 

 were left on the balance pan. 



after 13 min. lost 35.4% fresh weight 



23 " " 58.2% " 



31 " " 71.6% " 



37 " " 80.3% 



At the end of 50 minutes they had lost all the water that would 

 evaporate under the existing conditions of temperature and 

 humidity. 



I have not attempted to interpret these figures yet, as to what 

 they may mean in connection with vitality of seedling due to 

 loss of water. It seems as though the White pine seedlings three 

 years old could withstand at least a 10 per cent loss of fresh 

 weight, and that by far the larger part of the loss occurs from 

 the roots. From some other work that we have done I am led 

 to suspect that the age of the seedling will affect the rate of loss, 

 and very probably the condition of the roots at the time of tak- 

 ing from the ground exerts a large influence upon the rate of 

 evaporation, the more white tips the more rapid the loss. 



