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 on 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 worth 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. V. Theobald. 



Gatton Park, Sueeey, 



2Wi July, 1902. 



To Peofessor Laxkestee, 



British Museum (Nat. Hist.) 

 Cromwell Road, S.W. 



Dear Sie, — 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 larvae of the Sciarin^ being harmful. Under the 

 circumstances, and as it seems certain that the Coliembola 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 compcst 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 



