Altlhoughl cutimize(d tissue in some forlmi is the first harrier to the entrv of chemicals into plants, dlirect measurements of the permeability properties of cuticular membranes are limited aandl qualitative (1, 5 ). Froml clirect miieasuremleints oin isolated cuiticle Skoss (9 ) has reported that Eniglish ivy leaf cuticle is relativelv illmpermleable to w ater, aandl that lemloni leaf cuticle is impermeable to the sodiunm salt of 2,4-dichlorophenoxyacetic acid, to the ammiioolniunm salt of dIinitro-o-sec-but lplleinol. andl to silver and chloriOle ionls. Similarly Orgell (7 )

A penetration test with plant leaf cuticle membranes was used to measure the effect of surfactants (anionic, cationic, and nonionic) on the permeability of leaf cuticle to a slowly penetrating compound (sucrose) and a rapidly penetrating compound (N-isopropyl-achloroacetamide). Mixing surfactants with these compounds altered their penetration little, if at all, and even prior soaking of the cuticle disks in 1 % solutions of the surfactants or sodium hydroxide increased the penetration of the -chloroacetamide slightly in only one case.Prior soaking of the cuticle disks in chloroform, however, increased the permeability of leaf cuticle to the acetamide markedly. It is concluded that although cuticle permeability can be modified, the surfactants currently used commercially in pesticide formulations do not exploit the opportunity to alter the permeability of hydrated leaf cuticle.

A recent demonstration of the production of yeast from hydrocarbons1.2 has been publicized because of the contribution it might make to the world food problem.3 It is also becoming increasingly evident that end-product accumulation is not completely dependent on the starting substrate,* and that it might be possible to replace some carbohydrate fermentations with hydrocarbon fermentations giving the same product, if the substitution can be justified economically. This communication attempts an evaluation of a general characteristic of aerobic fermentations to assess the relative merits of biosynthesis from hydrocarbon and carbohydrate starting materials.A major factor in aerobic fermentation is oxygen transfer from the gas phase to solution in the proximity of the cell! Although it, can be rationalized that oxygen transfer is the rate limiting step in aerobic fermentations,S this generality has been opposed.? It is considered a reasonable assumption, however, in fermentations such as yeast propagation,? where deBecze and Liebmanns consider aeration the most important factor accounting for 10-2094 of the total production cost.If we accept the premise that in yeast propagation oxygen transfer limits the production rate, then it is pertinent to examine the oxygen requirement of a hydrocarbon fermentation directed at yeast production. In the following calculations these assumptions are made :The composition of the product from the carbohydrate and hydrocarbon fermentations is identical.A typical microbial composition is 47% carbon, C; 6.57, hydrogen, H; 7.5% nitrogen, N ; 8% ashg; and 31% oxygen, 0, by difference.The dry weight yield of yeast from carbohydrate is 5094.9v10The dry weight yield of yeast from hydrocarbon is l0O%,.ltl1

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