1910.] PUBLIC DOCUMENT — No. 31. 227 



it would seem desirable to determine whether short exposures 

 to greater strengths would be effective against the insects. 

 Until this is determined it is probable that the best treatment 

 for the white fly on tomato plants is to fumigate them with a 

 strength of .015 gram of KCN per cubic foot for a })eriod of 

 from forty-five minutes to one hour, on a dark — moonlight, 

 or perfectly cloudy • — night, in a house where the humidity is 

 below 70 degrees at the beginning of the treatment. Fumiga- 

 tion in this way will probably slightly injure the plants and 

 may cause curling of the leaves; but the injury will be less 

 than would be that caused bv the insects if there were no treat- 

 nient given, and three such treatments at intervals of twelve 

 days should not prove serious to the plants, while they should 

 reduce the white fly to a negligible quantity for quite a period, 

 — probably until after the crop has been gathered from the 

 plants concerned. 



IT. CUCUMBERS. 



BY CHARLES W. HOOKER, PH.D. 



Introduction. 



BY H. T. FERNALD. 



The experiments on cucumbers which follow were made dur- 

 ing the year 1907 by Dr. Charles W. Hooker as a portion of 

 his graduate work at the Massachusetts Agricultural College. 

 More time being available for the purpose than was the case 

 with the tomato tests, it was possible to make the tests more 

 exhaustive, but the general ideas were the same for both series 

 of experiments. 



The two most common varieties of cucumber gro"wii under 

 glass in Massachusetts were used, viz., Rawson's Hothouse and 

 White Spine. The latter variety seemed, on the whole, to 

 ])roduce the better plants. Two plants of each variety were 

 used for each test. 



The supervision of this work fell upon the writer of this 



