168 REPORT 4, UNITED STATES ENTOMOLOGICAL COMMISSION. 
pulverized should not exceed one pound at a time, thus avoiding too 
high a degree of heat, which would be injurious to the quality of the pow- 
der. The pulverization being deemed sufficient, the substance is sifted 
through a silk sieve, and then the remainder, with a new addition of 
flowers, is put in the mortar and pulverized again. 
The best vessels for keeping the powder are fruit jars with patent 
covers, or any other perfectly tight glass vessel or tin box. 
The use of py^etheum as an insecticide.— Up to a compara- 
tively recent period the powder was applied to the destruction of those 
insects only which are troublesome in dwellings, and Mr. C. Wiliemot 
seems to have been the first, in the year 1857 (?), to point out its value 
against insects injurious to agriculture and horticulture. He goes, 
however, too far in his praise of it, and some of his statements as to 
its efficacy are evidently not based upon actual experiment. Among 
others he proposes the following remedy: "In order to prevent the 
ravages of the weevil on wheat fields, the powder is mixed with the 
grain to be sown, in proportion of about ten ounces to about three 
bushels, which will save a year's crop." This is simply ridiculous, as 
every one who is familiar with the properties of Pyrethrum will under- 
stand. We have during the past few years largely experimented 
with it on many species of injurious insects, and fully appreciate its 
value as a general insecticide, which value has been greatly enhanced 
by the discovery that it can be most economically used in liquid solu- 
tion ; but we are far from considering it a universal remedy for all in- 
sects. No such universal remedy exists, and Pyrethrum has its disad- 
vantages as has any other insecticide now in use. The following are 
its more serious disadvantages: (1) the action of the powder, in what 
ever form it may be applied, is not permanent in the open air. If 
e.g., it is applied to a plant, it immediately affects the insects on that 
plant with which it comes in contact, but it will prove perfectly Harm- 
less to all insects which come on the plant half an hour (or even 
less) after the application; (2) the powder acts in the open air — unless, 
perhaps, applied in very large quantities — only upon actual contact 
with the insect. If, e.g., it is applied to the upper side of a cotton leaf 
the worms that may be on the under side are not affected by it; (o) it 
has no effect on insect eggs, nor on pupae that are in any way pro- 
tected or hardened. 
These disadvantages render Pyrethrum in some respects inferior to 
arsenical poisons, but, on the other hand, it has the one overshadowing 
advantage that it is perfectly harmless to plants or to higher animals ; 
and if the cultivation of the plants in this country should prove a suc- 
cess, and the price of the powder become low enough, the above men- 
tioned disadvantages can be overcome, to a certain degree, by repeal, d 
applications. 
It is to Prof. E. W. Ililgard, of the University of California, that we 
