Ll. Lloyd 27 



The amount of cyanide which should be put into one jar depends on 

 the width of tlie liouses which vary in the Lea Valley from 12 to 30 feet. 

 A good rule to follow is to so arrange the jars that the distance between 

 two is approximately the width of the house as this arrangement gives 

 an even distribution of the gas. Quarter ounce charges are recommended 

 for houses up to 14 ft. wide, half ounces for houses 14-20 ft. wide, and 

 ounces for wider ones. It is not wise to use a larger charge than this in 

 tomato houses as the concentrated gas evolved so close to the plants is 

 liable to cause damage. 



The use of liquid hydrocyanic acid has recently been advised by 

 Quayle(7) for the fumigation of fruit trees as an alternative to the jar 

 method of generation, but the difficulties of distribution make this 

 impracticable in large greenhouses. 



Repetition of fumigation. The fumigation should be repeated when 

 all the eggs have hatched but before any of the young can become adult. 

 A reference to Table III shows that at any temperature there is an 

 interval of a few days between these periods in heated greenhouses. The 

 most suitable days for the second fumigation are shown in the poster 

 ''Cyaniding Tomato Houses." 



Effect on plants. While the doses of cyanide mentioned above may 

 be applied without hesitation to most greenhouse plants, very consider- 

 able caution is required in applying them to tomatoes, whether growing 

 in pots or in borders, as this plant is particularly susceptible to damage 

 by the gas. Hard growing wiry tomato plants resist the gas much better 

 than soft sappy ones, but in trade nurseries the plants are usually of the 

 latter type (Plate I, fig. 3). 



The damage to which they are liable consists of burns on the fohage 

 which may develop at once or several days after the fumigation. The 

 damage is symmetrical on the leaflets and in moderate cases is confined 

 to the basal half on each side of the midrib. Leaves which are fully 

 grown are much less liable to damage than the younger ones. In mild 

 cases the leaflets of the younger leaves crinkle up without any browning. 

 On several occasions the only damage which has occurred has been a 

 scorch on the underside of the petioles of two or three leaves which 

 causes a permanent dwarfing of the leaf. The leaflets develop normally 

 but become very crowded, while sometimes the leaf coils spirally round 

 the main stem. The growing points and stems and trusses are only 

 damaged by exaggerated carelessness such as fumigating in dayUght or 

 by the use of excessive doses. Faulty setting of the fruit could never be 

 associated with fumigation. 



