Abstract

                                Investigations reported in the earlier articles (Satyanarayana, 1951), showed that the amount of DDT recovered from the surfaces of apple leaves varied with the mode of deposition, the nature of the solvent used, and the concentration of the insecticide in the preparation. The nature of the emulsifer used had but little effect, the percentage of the solvent in the preparation and the nature of the surface (upper or lower) though having some slight effect did not appear to be of much consequence. Though under the experimental procedure adopted in the present investigation it has not been possible to recover all the DDT initially deposited, it was shown that either by pro- longing the period of shaking or by continued extraction in a soxhlet cent percent recovery was possible. It was, therefore, clear that the material that was not recovered was not lost by any other process like the catalytic decomposition by leaf tissue, etc., but could be recovered. Absorption of insecticides into the plant tissue is not a new idea. Swain (1933), working with petroleum oils observed this and suggested a differentiation between the available' i.e. the insecticidally useful, and the non-available or the locked up portions. Probably, a similar differentation needs to be made in the case of DDT also, In a way this fact seems to have been realized by Barlow and Hadaway (1949), when they designated the two fractions of DDT as 'inner' and outer.

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