2, BULLETIN 1201, U. S. DEPARTMENT OF AGRICULTURE. 



vated; (2) characteristics of growth, whether annual or perennial, 

 large or small, abundant or sparse ; (3) portion of the plant effective ; 

 and (4) nature of the active constituent and the means necessary to 

 make it available for use. 



The most desirable type of plant is no doubt one which grows 

 abundantly in a wild state, preferably in areas not readily adapted 

 to the cultivation of valuable crops. Under such conditions the 

 material could be obtained with the minimum of expense, the only 

 cost being that of collection and preparation. Less abundant growth 

 involves greater cost in collecting, and in case the plant must be 

 cultivated it must bring sufficient return to compete with other 

 crops adapted to that particular region. Perennials are much more 

 desirable than annuals, since their products can usually be collected 

 from year to year. Leaves and branches of trees or shrubs or the 

 entire herbaceous portions of hardy perennials can be most economi- 

 cally obtained. On the other hand, the collecting of fruits or seeds 

 or the digging of roots or rhizomes can, as a rule, be much less 

 economically done. In the case of small plants, gathering the 

 roots usually means the destruction of the plant, which, in time, is 

 likely to reduce the supply unless the plant is under cultivation. 



The character of the active constituent has an important bearing 

 on the handling necessary in its preparation for the market. Sub- 

 stances like alkaloids and toxic resins are usually not subject to ready 

 decomposition, and material containing such constituents need not 

 be dried and handled with more than ordinary care. On the other 

 hand, plant material depending for its action on glucosides must be 

 carefully dried in order to inhibit decomposition of such constituents. 

 In the case of plants native to foreign countries, especially the 

 Tropics, this is an important matter, since the collecting is usually 

 done by natives, and control of conditions of handling is likely to 

 be difficult. Long voyages, especially by sea, are furthermore likely 

 to cause deteriorating changes in such plant materials. 



It is evident, therefore, that the search for a plant which may be 

 made commercially available as an insecticide at a reasonable price 

 extends much farther than merely finding a plant which possesses 

 insecticidal properties to a satisfactory degree. It involves, in addi- 

 tion, a study of the botanical characteristics of such a plant, its 

 habitat, the available natural supply, the means necessary for its 

 proper collection and shipment, and, above all, the cost at which 

 it can be delivered to the manufacturers in this country. 



METHODS USED BY THE WRITERS IN PREPARING PLANTS 

 FOR INSECTICIDES. 



To determine the insecticidal properties of plant material, a num- 

 ber of different ways of preparing it are necessary. This is espe- 

 cially true if the material is of unknown composition. Tests on in- 

 sects may be made by applying the material (1) in a dry, finely 

 ground condition as a dusting powder; (2) in the form of water ex- 

 tracts made with hot or cold water; or (3) as extracts made with 

 other solvents, such as benzene, gasoline, petroleum ether, and alco- 

 hol. In all cases the material must be thoroughly dry, and then be 

 reduced to a powder. If the powdered material is to be used as such 



