66 



work was done injured. In fact, from the results of fumigating plants 

 before setting them out, we believe that strawberry plants in the field 

 would stand a strength of two-tenths or three-tenths of a gram KCn 

 per cubic foot for twenty or twenty -five minutes, were that necessary. 



AVork done with a wooden box 2 by 2 by 2^ feet, with open bottom, 

 in fumigating loose strawberry plants infested with Aphis forbesl 

 brought out the influence of the soil on the gas and the ready diffu- 

 sion in a cu])ical space. In this box two-tenths gram KCn per cubic 

 foot in ten minutes, three-tenths gram in five minutes, and one-tenth 

 gram in twenty minutes proved fatal to the aphides. 



Thus, in the 10-foot frame, with a soil surface of 20 square feet and 

 a cubic capacity of 8i feet, or a ratio of 2i soil surface to 1 of vol- 

 ume, just twice as much gas was required to be generated from two 

 points to be effective as that in the wooden box of 10 cubic feet 

 capacity and 5 square feet soil surface, having an almost opposite 

 ratio of 2 volume to 1 of soil surface. Again, the covers for indi- 

 vidual plants, with a soil surface of about 3 square feet and a capacity 

 of one-half cubic foot, or a ratio of 6 soil surface to 1 of capacity, 

 required eight-tenths gram per cubic foot, or four times as much. 

 Comparing these figures with the results obtained in the laboratory 

 test of the influence of the soil, by a rough calculation a rule some- 

 what as follows might be deduced: Let x equal the mean height 

 in feet: then the amount of cyanide of potassium per cubic foot 

 expressed in decigrams would be 2 plus the reciprocal of ,t, or the 



decigrams of KCn to be used per cubic foot equals 2+— • 



Whether these ratios would hold true for a larger series of tests 

 remains to be ascertained, but they at least indicate the general tend- 

 ency of the diffusion of the gas and the influence of the soil upon it. 

 The cost of such frame is but little. The materials for them should 

 not cost over 25 or 30 cents, and they are easily made. With rows 3 

 feet apart, using 12 frames, with three-tenths gram per cubic foot for 

 ten minutes, an acre could be covered in about two da3^s at a cost of 

 about $3 for chemicals. This treatment is practicable, therefore, only 

 upon plants of some considerable value and for relatively small areas. 

 Under many circumstances, however, it could be used to much better 

 advantage than any other means of combating a pest, and often might 

 be found effectual where no other method of extermination were 

 possible. 



NOTES FROM DELAWARE. 



By E. DwiGHT Sanderson, Newark, JJel. 



T/i> harlequin cahbage hug. — ^The harlequin cabbage bug has l)een 

 under observation as much as the scarcity of material would permit. 

 Last year the bugs were not noticed till late in the summer, and injury 

 by them, as noted in one or two instances, was confined to very late 



