184 Bulletin 190. 



nor were any of the caterpillars or puj)a% but nmcli damage was 

 done to the young growth on roses, carnations and chrysanthemnnis, 

 and geraniums were considerably injured ; perhaps some of the 

 injury to the plants was due to the fact that the fumigation was 

 done in the daylight. Some infested cinerarias were then placed in 

 a tight, dark fumigating box and subjected to the fumes of this 

 deadly gas, using the cyanide at the rate of .15 grams per cubic 

 foot (strongest dose recommended for greenhouses) for half an hour, 

 llesult, plants not injured, and even the smallest or one-third grown 

 caterpillars were as lively as ever ; some plant-lice, tlirips and 

 mealy-bugs, which were also on the plants, were all killed. Half an 

 hou.r later one of the cinerarias containing tlie same young cater})il- 

 lars, some full grown caterpillars, and a pupa was subjected to the 

 gas at double the above strength (using .3 grams of the cyanide per 

 cubic foot) for half an hour. Kesult, the small caterpillars only 

 were killed, and the blossoms of the plant were injured ; the large 

 caterpillars and pupa were apparently unaffected. We must con- 

 clude, then, that our experiments thus far indicate that the green- 

 house leaf-tyer will not succumb to the amount of hydrocyanic acid 

 gas which can be generated in a greenliouse with safety to the 

 plants. 



Finally, the oidy method by which they have thus far been able 

 to materially reduce the numbers of the pest in the horticultural 

 greenhonses is by hand-picking or killing. AH hands are constantly 

 on the lookout for signs of the insect, and every specimen of moth, 

 caterpillar or |)upa found is at once killed. Forty of the moths 

 have been killed in one morning in the houses, and scarcely a day 

 j^asses that many of the leaf-tyers are not thus sent to their "happy 

 hunting grounds." The moths are quite easily caught or crushed in 

 their resting places, an<l the caterpillars are, readily located by their 

 work on the leaves, and by a constant warfare of this kind the pest 

 can 1)0 kept below the danger limit ; but, as those who have had 

 experience know, the few remaining stragglers can often anriuy the 

 lover of ])erfect-leaved, symmetrical })lants more than a host of 

 plant-lice, mealy-bugs or scale insects. 



MARK VERNON SLINGERLAND. 



