262 EXPERIMENT STATION RECORD. 



A few experiments with crude iietruleuni as a remedy for San Jose scale on pear 

 trees indicated that a 25 per cent jnechanical mixture was as effective as nndihited 

 petroleum. 



Biological and economic notes are given on Mesograpta polita, Myzus porosux, a 

 number of insects injurious to clover, horse hots, striped cucumber beetles, boll- 

 worm, harlequin cabbage bug, and corn root-louse. 



A paper on hydrocyanic-acid gas as an insecticide for low-growing plants has been 

 previously noted (E. S. E., 12, p. 861). 



The diffusion of hydrocyanic-acid vapor in an inclosed space is discussed by C. L. ' 

 Penny. Preliminary experiments in taking samples of air from fumigating rooms 

 were made by the use of 5-gallon Seltzer bottles, from which the air was exhausted 

 and into which the gas could be admitted by a movement of the stopcock. Analysis 

 of the air and gas mixture thus obtained indicated that immediately after the genera- 

 tion of the hydrocyanic-acid gas there is an excess of gas around the generator. 

 Within 2 minutes' time this excess disappears, leaving only one-third of the normal 

 quantity of gas near the generator, while 21 times the normal quantity is found at 

 the opi^osite end of the fumigating box. This excess rapidly diminishes and the gas 

 increases in density around the generator so that a tendency toward equilibrium is 

 noted, although more than 20 minutes is required for the establishment of a perfect 

 equilibrium. These experiments were conducted in a box A\ith a capacity of 60 cu. 

 ft., wdth dimensions 8 by 3 by 24 ft. Similar experiments were made in boxes of dif- 

 ferent sizes and shapes, and it is concluded that in spontaneous diffusion within a 

 closed space the quantity of hydrocyanic-acid gas at a given point may be as low as 

 23 per cent of the normal quantity and as high as 27.2 per cent. Inequality does not 

 persist for a great length of time, but is sufficient to render it certain that the amount 

 of cyanid of potassium used per cubic foot is no guarantee of a sufficient amount of 

 gas in all parts of the space to be fumigated, or of too little to injure the i:)lants. 



Experiments in a room 20 by 19 by 10 ft. indicated that when a generator is placed 

 near one wall, the gas rises vertically from the generator and, following the ceiling, 

 descends on the opposite side of the room and completes the circuit by returning 

 along the floor. Of the total amount of hydrocyanic-acid gas, about 5 per cent 

 remains in the generators, 7 per cent is lost by leakage or surface condensation on the 

 walla of the room, while 88 per cent is diffused and becomes effective for insecticide 

 purposes. 



The results of these experiments were made use of in further experiments in fumi- 

 gating boxes. It was found that when gas was allowed to diffuse spontaneously 

 from 1 generator, the diffusion was very unequal for a considera])le length of time, 

 and that it was i)ossi):)le for an animal like the guinea pig to live at least 37 minutes 

 in the fumigation l)ox. It is recommended that the generator be placed below the 

 part of the fumigating box which contains the plants and that communication be 

 made by means of numerous slits, so as to insure the rapid and equal diffusion of 

 the gas. 



Insect attacks in 1900, R. S. MacDougall {Tram. Hkjhland and Agr. Soc. 

 Scotland, 5. ser., 13 {1901), pp. 296-305, figs. 7). — Phyllopertha horticola is described in 

 detail in its various stages. The adult beetle injures forest and orchard trees by 

 feeding upon the leaves. The eggs are deposited in the soils of gardens and grass 

 lawns, and the grass and fruit are injured chiefly by attacks ujjon the roots. It is 

 recommended that adult beetles be shaken from trees early in the morning into 

 some catching apparatus, and that infested soil be treated with from 3 to 4 tons of 

 gas lime per aci'e. 



Onion fiy {Phorbia ceparum) is reported as having caused considerable injury 

 during the year. Brief notes are given on the life history of the species. Infested 

 plants may be recognized by the leaves changing to a yellow color. For combating 



