MATERIALS 57 



Quassia and Pyrethrum. All these, however, except 

 Nicotine, are subject to the drawback of being diffi- 

 cult to prepare so as to be of known or constant 

 strength. 



25. Hellebore. — This is a light yellowish-brown 

 powder obtained by grinding up the roots of V^era- 

 trinn album or V. viride. It is useful as an insecticide 

 for sawfly larvae, and, being less poisonous than arseni- 

 cal compounds, it may often be used in cases where 

 the latter would involve the danger of poisoning the 

 fruit, as, for instance, in the case of the gooseberry 

 sawfly (p. 83). It may be used as a powder, dusting 

 it over the bushes, in which case it may be con- 

 veniently mixed with twice its bulk of some other 

 powder, such as plaster of Paris, lime or flour — the 

 last of which is stated to make the hellebore adhere 

 better — or it may be sprayed on to the bushes, mixed 

 with water, in which case 3 or 4 ozs. should be mixed 

 with every 10 gallons of water. It may also be used 

 mixed with paraffin emulsion. 



Hellebore deteriorates on keeping, and the samples 

 used should, if possible, be freshly prepared. 



26. Nicotine ( Tobacco^ — This, on the whole, appears 

 to be the most effective of the vegetable poisons for 

 destroying psylla, aphis, woolly aphis, etc., but, accord- 

 ing to the experiments at Woburn, it does not 

 compare favourably with a weak paraffin emulsion 

 (9<^, \6d, etc.) for the destruction of caterpillars, except 

 when used in excessive quantities. It presents the 

 advantage, however, of being harmless to trees when 

 these are in full blossom, which paraffin is not ; more- 

 over, it can never harm the foliage, which paraffin 



