268 Journal of Agricultural Research voi. xv, No. s 



The percentage of old leaves lost, as given in the tables, is neither dis- 

 tinctly correlated with conditions under which the plants were fumi- 

 gated nor with the dosage given. Whether this discrepancy is due to 

 specific resistance of the different species of Cattleya fumigated or to 

 physiological conditions of the plants at the time of fumigation remains 

 to be determined by the use of known plants kept under similar condi- 

 tions before exposure to the gas. It will be noted, however, that plants 

 which lost a high percentage of old leaves produced flowers, new leaves, 

 and pseudobulbs. (PI. 19.) 



FUMIGATION AS A REQUIREMENT FOR ENTRY 



Owing to the large number of insects which have been intercepted in 

 cases of orchids and to extremely poor inspection facilities at the ports of 

 entry, the Federal Horticultural Board has instructed its inspectors to 

 require the fumigation of all orchids arriving in bulk from countries 

 which do not maintain a recognized inspection service. On the strength 

 of the experiments listed in this paper, all plants fumigated in the orig- 

 inal container must be fumigated with i ounce of sodium cyanid, with 

 an exposure of one hour. A preliminary vacuum of 20 inches is required 

 prior to the generation of the gas. 



CONCLUSIONS 



(i) Black areas appear on unfumigated as well as fumigated leaves 

 which have been injured. 



(2) Progressive yellowing occurs on both unfumigated and fumigated 

 plants and depends on adverse treatment or age of the leaves. 



(3) Fumigated plants lose their leaves more rapidly than do unfumi- 

 gated plants when subjected to adverse treatment. Young leaves and 

 shoots are not severely injured by the gas with a i -ounce dosage, although 

 a number of old devitalized leaves may fall. 



(4) Fumigation is not responsible for dying of pseudobulbs, if exces- 

 sive dosages are not used. 



(5) Presence of water on cattleya leaves does not increase burning from 

 fumigation. 



(6) Loss of a few old leaves does not render a plant valueless, as in a 

 brief period they are replaced by new vigorous foliage. 



(7) Where excessive dosages are not employed, orchids are apparently 

 stimulated by hydrocyanic-acid gas. (See PI. 19.) 



(8) Infested orchids at the time of arrival at the port of entry, if in a 

 reasonably good condition, are not seriously affected by hydrocyanic- 

 acid gas generated at the rate of i ounce of sodium cyanid per 100 cubic 

 feet, and are not killed where a 4-ounce dosage is used. 



(9) Insects which are not hermetically sealed in stems or pseudobulbs 

 of cattleyas can be killed in the original cases with hydrocyanic-acid gas, 

 provided a preliminary 20-inch vacuum is given. 



