Excerpt from Plants Tested for or Reported to Possess Insecticidal Properties

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 hard perennials can be most economi cally obtained. On the other han 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. Oh 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.

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