August, '11] WOODWORTH: FUMIGATION TENT LEAKAGE 377 



This close may be considered as ample or perhaps a little high, for 

 the reason that it represents the average of all fumigation work though 

 some of it (not a very large amount, however) was for red and purple 

 scale work, both of which usually receive more than the black scale, 

 and because fumigators would be more liable to give more than neces- 

 sary since a slight injury to the tree is not considered as bad as a 

 failure to kill the scale. 



The measurements also gave data showing that the rate of increase 

 of dose for larger trees and of decrease for smaller ones did not corres- 

 pond with the changes in volume. While there was a great deal of 

 diversity in the practice of different fumigators, they agreed in the 

 one fact that the rate of change in dose was strikingly less than the 

 rate of change in volume. 



The suggestion made at that time based on the results of this study 

 was that the area of the surface of the tent instead of the volume 

 enclosed might be adopted as the measure of the dose. This sugges- 

 tion has been followed by several writers and experimentors and is 

 today the only basis of calculation that approximates the actual aver- 

 age practice. 



At the time the above suggestion was made, it was clearly under- 

 stood that the area basis of calculation gave only an approximation 

 to the correct dose and did not by any means represent an accurate 

 allowance for any particular degree of leakage. A recent student 

 (Woglum) has offered a table calculated by the formula dose =vXv 

 which he supposed did accurately allow for leakage but of course is 

 only the area basis suggested by me years before. 



Last year in presenting the methods available for scheduUng trees 

 for fumigation, the need of some method of measuring the leakage of 

 tents and of accurately adjusting the dose to the leakage became very 

 evident. Accordingly the present season over 5,000 determinations 

 were made in the field of the leakage of fumigation tents in actual 

 operation and in many cases of the same tent under varying weather 

 conditions. The details of these results cannot be given at this time 

 and we shall limit ourselves to the one problem of the apphcation of 

 the averages thus obtained to the production of a table of dosages. 



Of course such a table must be taken as only an approximation 

 but there seems to be sufficient data at hand to warrant us in consid- 

 ering this table accurate enough for practical use. 



The other problems concerned are now the subject of investiga- 

 tion and will be presented in due time. 



In the absence of accurate experimental data relative to the laws 

 governing the escape of gases through such a net work as presented by 

 the weave of a fumigation tent, we are forced to the assumption that 



