Insects in Orchid Houses . 
1 1 1 
with some common orchids and hydrocyanic acid gas. This gas can be 
used for such delicate plants as maidenhair fern without injury and is 
fatal to all forms of animal life, but its effect on orchids has not been 
observed. If there is much moisture oil the plants this gas loses much 
of its potency, and the air during fumigation should be dry. Its effects 
in an orchid house might not therefore be as successful as under other 
circumstances. It is certainly w T orth trying, however, as fumigation with 
tobacco, etc., would have little effect on these creatures that are causing 
the annoyance. 
Great care should be exercised in the use of hydrocyanic acid gas, as it 
is a most dangerous poison to man. 
Should Mr. Colman think it advisable to experiment with this 
insecticide, information as to procedure can be sent him. 
There does not seem to be any other way in which these pests can be 
eradicated under the conditions necessary for orchid cultivation. 
Fred. Y. Theobald. 
Gatton Park, Surrey, 
29th July , 1902 . 
To Professor Lankester, 
British Museum (Nat. Hist.) 
Cromwell Road, S.W. 
Dear Sir, — In further reply to the interesting report of Mr. 
Theobald of the 21st, I have had an opportunity of a careful discussion 
of the points raised with my gardener. 
I understand the report to throw considerable doubt upon the 
probability of the larvrn of the Sciarinse being harmful. Under the 
circumstances, and as it seems certain that the Collembola or Spring-tails 
are, I suggest that we ignore the former, especially as we have not been able 
to observe them and have no actual evidence of their causing mischief. 
There will be no difficulty in adopting the suggestion that the effect 
of hydrocyanic acid gas upon orchids shall be ascertained by experiments. 
It is believed, however, that, used in moderation, it will not be harmful to 
them. It is certainly unfortunate that its effect is likely to be minimised 
by moisture. The moisture on the moss, etc., can be reduced, but it is 
such an essential feature in the early stages of orchid growing that it 
would have to be done with great care and not for any length of time. 
Should it be the young Spring-tails which are most largely responsible for 
the mischief, material relief from these pests might be secured by an 
application of the gas before the seed is sown or before the germinating 
plants are transferred thereto and when the compost is in a perfectly dry 
state. A good deal depends upon their habits, but I am writing on the 
assumption that the young may not develop very quickly or be able to 
reach the pots before the plants are sufficiently strong to take care of 
themselves. It seems difficult to place the pots in such a position as to be 
out of reach of the adult Spring-tails, but we will gladly experiment if any 
suggestion can be made. We have now placed some of the pots on a zinc 
tray on stands, which seems to have minimised the mischief somewhat. 
Although the more orthodox way of raising the seed seems to be to sow it 
