THE IN.inaOUS SCALE lysECTS AND 3IEALY BUGS, &c. 257 
cloth. He imiiiediately withdraws, and the men shovel a little soil on 
the edges of the cloth all around, to more thoroughly prevent the escape 
of the gas. 
" The rapidity of the evolution of the gas depends largely upon the 
size of the pieces of cyanide. If these are like powder, the reaction 
is violent and immediate ; but if in lumps, the reaction takes place more 
slowly and continues for a minute or longer. The slow^ reaction is 
desired, partly because less injury results to the foliage immediately 
above the vessel. But the lumps must not be too large, for then the 
reaction is liable to be imperfect owing to a black coating (carbon ?) 
forming over the lumps and preventing further decomposition by the 
acid. The water should not be added too soon, or part of the cyanide 
becomes dissolved and gives a violent reaction. The residue which 
remains in the dishes is buried, and the dishes are washed in clean w^ater 
before being again used. 
" Time Xecessarij for Treatment. — The cover is left over the tree for 
thirty minutes in the case of small trees, and forty-five in the case of 
those over twelve feet in height. At the expiration of this period the 
generating vessel is removed and the residue buried in the soil. 
" A number of trees are fumigated together, the endeavour being to 
treat as many at a time as can be covered and uncovered during the 
period of exposure. In this way the men are kept continuously busy, the 
time for the removal of the first tent arriving by the time that the last 
tree is covered. 
Abs£}ice of Sunlight Necessary. — The originators of the fumigation 
process observed that the gas was most efficacious, and that less injury 
resulted to the foliage, when the operations were performed at night than 
when they were carried on in sunlight. It is said that chemical changes 
are produced in the gas by the action of sunlight, and that the resulting 
gases are more injurious to the plant life and less to animal than 
hydrocyanic acid gas. Whether or not these theories are correct is of 
small practical importance, for the foliage of a tree will suiter serious 
injury if the tree is left covered with an air-tight oiled tent for half an 
hour in sunlight without the gas being present. Having ascertained this 
fact by experience, the foreman in charge of the Board's outfit refrained 
from covering trees until the sun had sunk from sight on any but cool, 
dull days. The great majority of the trees treated have been fumigated 
after sunset. The ideal night for fumigating is quiet, cool, and moon- 
light, and without dev*^." 
From such valuable and trustworthy evidence as the foregoing, we 
may safely take action with consignments of hard-wooded plants. But 
for such tender things as Orchids or other rare and costly plants, the 
process is likely to end in serious injury to them, and cannot therefore 
be expected to find imiversal favour amongst English horticulturists. 
There is this to be added, however, that all other fumigating compounds 
have been found hj Mr. Green less efl'ectual to coccids and more 
injurious to plant life than the hydrocyanic acid gas. 
In the absence of fumigation or of the application of insecticides which, 
owing to the nature and condition of the plant, may be deemed advisable, 
a thorough sponging with clean water should invariably be made. All 
