THE TEINCirAL INSECTICIDES. 19 



more dangerous to have around than either of the 

 above highly colored substances ; and unless applied 

 as soon as it is mixed with water is very liable to 

 burn the foliage. 



The principal substances used for killing insects, 

 by contact, are the following : 



Hellebore is a powder made of the roots of a plant 

 called white hellebore (Vemtrum album). It is a veg- 

 etable poison, but much less dangerous than the 

 mineral, arsenical poisons, and kills both by contact 

 and by being eaten. It may be applied as a dry 

 powder or in water, an ounce to three gallons. It 

 retails at about twenty-five cents per pound, and is 

 especially excellent in destroying the Imported Cur- 

 rant Worm. 



Pyrethrum is an insecticide of recent introduction, 

 made from the powdered flowers of plants of the 

 genus Pyrethrum. There are three principal brands 

 upon the market, known as Persian insect powder, 

 Dalmatian insect powder, and Buhach — the latter 

 being a California product. The greatest obstacle to 

 the use of Pyrethrum has been the difficulty of ob- 

 taining the pure, fresh article. After long exposure 

 to air it seems to lose much of its insecticidal value. 

 Hence dealers should purchase a fresh supply each 

 season, and should keep it in air-tight vessels. Py- 

 rethrum is used mainly as a dry powder or in water 

 (one ounce to three gallons) ; but may also be used in 

 the form of a tea, or a decoction, a fume, or an alco- 

 holic extract diluted. For use as a dry powder it 



