THE AMERICAN ENTOMOLOGIST. 



43 



portion most likely to give general satisfac- 

 tion by effectually destroying the worms 

 without injuring the plants. 



All that has been said under the head 

 of Paris green as to the desirability of 

 adding a small quantity of flour or other 

 substance to give adhesiveness to the liquid 

 will hold equally true of London purple, 

 but the latter has in many respects a great 

 advantage over the former, especially in 

 its greater cheapness, being a mere refuse 

 which, from its poisonous nature, was a 

 drug to the manufacturers and had to be 

 gotten rid of by being dumped long dis- 

 tances out at sea. This substance can be 

 put upon the market at the bare cost of 

 transportation. It can be sold in New 

 York at the low rate of 6 cents per lb., and 

 there is no reason why it should not be 

 obtained at any of the large shipping points 

 in the South at figures ranging between 7 

 and 10 cents a pound. This means virtu- 

 ally that the cost of destroying the worms 

 by this powder is reduced to such a mini- 

 mum as to depend mainly on the labor 

 and the other ingredients or diluents em- 

 ployed ; in other words, that, while the 

 planters, as heretofore, were obliged to pay 

 as much as $1 for the first cost of the 

 active poison needed for one acre, and 

 never less than 15 cents, he may now ob- 

 tain it for from 3 to 5 cents. 



London purple has this farther advan- 

 tage over other arsenical compounds 

 hitherto employed : Its finely-pulverized 

 condition seems to give it such penetrating 

 power that, when used in liquid, it tints 

 the leaves so that cotton treated with it is 

 readily distinguished at a distance, the 

 general effect being quite marked as com- 

 pai;ed with any of the other poisons simi- 

 larly applied. It seems also to be more 

 effectually absorbed into the substance of 

 the leaf, and is therefore more persistent. 

 At the same time experience shows that it 

 does not injure the squares any more than 

 Paris green. 



Pyrethrum Powder. 



The insecticide and insectifuge qualities 

 of the dried and finely-powdered flower- 

 heads of different species of Pyrethrum, 



and the harmlessness of the powder to 

 man, to other animals, and to plants, have 

 long since been known. Used against 

 various household pests under the names 

 " Persian Insect Powder " or " Dalmatian 

 Insect Powder," it has hitherto been put 

 up in small bottles or packages and sold 

 at such high prices as to preclude the idea 

 of using it on a large scale in the field. 

 The so-called Persian Powder is made 

 from the flowers of Pyrethrum carneum and 

 P. roseum, while that from P. cinerarice- 

 foHum, a native of Dalmatia, Herzegovina, 

 and Montenegro, is more generally known 

 as Dalmatian Powder. Some interesting 

 experiments made during the past year on 

 different insects by Mr. William Saunders, 

 of London, Ontario, show that the use of 

 this powder may be satisfactorily extended 

 beyond the household, while a series which 

 I made in the summer of 1878 with the 

 same powder on the Cotton-Worm showed 

 it to have striking destructive powers, the 

 slightest puff of the powder causing certain 

 death and the almost instant dropping of 

 the worm from the plant. Repeated on a 

 still more extensive scale the present year 

 at Columbus, Tex., the powder proved 

 equally satisfactory in the field. 



Here, then, we have a remedy far ex- 

 ceeding any other so far known in efficacy 

 and harmlessness to man and plant, and 

 the only question in my mind has been 

 to reduce its cost. There was some hope 

 of doing this by ascertaining the destruc- 

 tive principle, and it is to Prof. E. W. 

 Hilgard, of the University of California, 

 that we owe the first accurate determina- 

 tion of the same. The following extract 

 from a letter received from Professor Hil- 

 gard last September indicates the results 

 of some of his experiments : 



Dear Sir : Yours of 22d is to hand. I have 

 had Milco's product in hand for some time, and 

 have tried it on various bugs both in powder and 

 infusion. To understand the best manner of 

 using it in each case, it must be kept in mind : 



1. That the active substance is a volatile oil. 



2. That said oil, under the influence of air, 

 not only volatilizes, but is also oxidized, and 

 thereby converted into an inert resin. 



It follows from i, that the pyrethrum is at a 



disadvantage when used in the shape of powder 



j in the open air, especially when the wind blows ; 



1 from 2, that it is of the greatest importance that 



