1903] Robinson, — Insecticides used at Gray Herbarium 245 
obtained that these soft, sluggish, and supposably non-resistent crea- 
tures came out of a formaldehyde fumigation of many hours duration 
without any apparent injury, although the same treatment is known 
to kill with certainty the bacterial germs of anthrax, diphtheria, etc. 
From these experiments, it was inferred that, however valuable as a 
disinfectant, formaldehyde would be likely to prove an unsatisfactory 
insecticide, and further experimentation with it was accordingly 
abandoned. Others, by varying the method, may have greater suc- 
cess with it. 
In using carbon bisulphide, it should always be borne in mind that 
it is one of the most inflammable liquids known and that its vapor 
forms highly explosive mixtures with air. It is accordingly of the 
utmost importance for safety to keep both the liquid and vapor far 
from fire in any form or indeed from any source of heat, instances 
being on record in which carbon bisulphide has been ignited by the 
heat of steam pipes. It goes without saying that no match should 
be struck, lamp burned, or fire used in any manner in a room in 
which the fumigation is being conducted. The possibility of this 
easily inflammable agent acting chemically upon other substances 
employed in herbarium work and causing a heat-producing reaction 
sufficient to produce ignition, was early considered at the Gray 
Herbarium, and expert chemical advice sought. Happily, no such 
reaction appears possible with the other substances used. Where 
carbon bisulphide is to be used in quantity, it is a desirable precau- 
tion to store it in a remote out-building, bringing to the herbarium 
from time to time only such amounts as are to be used at once. The 
sulphide employed at the Gray Herbarium is kept in a small tool-shed 
at the back of the Botanic Garden. Some years ago it was kept in 
an old shed under a disused water tank, but one day the whole struc- 
ture suddenly collapsing freed many pounds of the sulphide, which 
for some hours threatened an unwelcome fumigation to the entire 
neighborhood. 
At the Gray Herbarium it has been found that no large group of 
vascular plants seems entirely immune from the attacks of insects. 
Probably the sedges are as little in danger as any ; grasses and ferns 
also, if kept in perfectly dry cases are little subject to such injury, 
although one of the worst cases of insect work which has come to 
attention was on a collection of ferns stored for some years in Trini- 
dad, doubtless in a damp atmosphere. Plants with a milky juice and 
