CHERMESID/E IN RELATION TO BRITISH FORESTRY. 155 



that the wood will remain free from these pests as, in most 

 cases, subsequent infection will take place, but it will ensure 

 that the further distribution of the Chermesidae will be limited, 

 and that the plants will get a chance to establish themselves in 

 their new environment. This is a very necessary precaution, as 

 my observations showed that the Chermesidae were frequently 

 widespread in forest nurseries, and that these pests often did 

 serious damage to their hosts immediately after a plantation has 

 been formed. My experiments have shown that the fumigation 

 of the nursery stock immediately before dispatch to the planting 

 area is an efficient method of killing the Chermesidae. This 

 fumigation can be carried out any time during the winter and up 

 to the I St April. The nursery stock is placed in a gas-tight 

 chamber and fumigated with hydrocyanic acid gas generated 

 from potassium cyanide at the rate of i oz. to loo cubic feet of 

 space, or from sodium cyanide at the rate of i oz. to 130 cubic feet 

 of space. This gas is highly poisonous but, provided reasonable 

 precautions are taken, the method is absolutely safe. The cost is 

 very small. This method could be used in any forest nursery 

 however small ; but it would be specially applicable if, in any 

 scheme of afforestation, large forest nurseries and depots for 

 distributing plants were established throughout the country. 



For a more detailed account of the biology of the spruce and 

 larch species, the reader is referred to my paper in the Royal 

 Society of Edinburgh's Froceedings for 1917, where also full details 

 will be found regarding the fumigation experiments. Appended 

 to the Royal Society paper is a full list of references on the 

 literature of the subject. 



In carrying out my researches, and in the preparation of this 

 paper, I have been indebted to the assistance of Prof. R. Stewart 

 MacDougall, the Hon. Consulting Entomologist to this Society. 

 I have also been indebted to Prof. I. Bayley Balfour, the 

 Hon. Consulting Botanist to the Society, for facilities for 

 observation and experiment granted in the Royal Botanic 

 Garden, Edinburgh. 



