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An attempt was made to explain the great variation in vitamin C content in garden crops, so that vitamin C content may be increased by altering the influencing factors. Ascorbic acid content (AA-ct) was estimated by titration with 2,6-dichlorophenolindophenol. Differences in AA-ct between plant varieties were attributed to polyfactorial genetic differences. Between the AA-ct's of (sub-units of) different genera no correlation with taxonomic order could be found.AA-ct of rose hips was correlated to the ratio K: Ca: Mg in ash. At the green stage AA-ct was highest when none of the cationic ratios deviated from the average. The same held for the coloured hips, but with other averages (higher K%) and higher AA-ct's. The ideal curve of AA-ct during fruit development may be modified by the weather. A maximum usually occurred in ripe fruit. In leaves it varied with incident solar energy; dehydroascorbic acid showed the opposite course.Growth substances strongly influenced both ascorbic acid and total vitamin C in the bark of cuttings and in germinating peas. After its formation from sugars, AA acts, particularly on chloroplast surfaces, as a transporter of H from chlorophyll. There it acts as a hydrogen donor and buffer.

A method was devised for estimating vitamin D in roughages. After boiling with 10 % alcoholic KOH the material was extracted with petroleum ether, and purified by chromatography through an activated alumina column with petroleum ether. Chromatography removed an unsaponifiable factor antagonistic to vitamin D. The eluate was assayed by the curative X-ray method against a vitamin D standard with white rats.No vitamin D could be detected in ensiled turnips. Average contents in roughages under Dutch conditions were: grass silage and artificially dried grass about 300 IU, hay cured in windrows and cocks 1000 IU, frame-dried hay 575 IU and straw possibly as windrow hay. Considering the usual rations and the great variation in vitamin D in hays the intake of the vitamin might not be adequate on all farms. Although identification of the antagonistic factor was not possible a relation appeared. to exist between the factor and carotene. Synthetic carotene and vitamin A palmitate 100-800 IU daily showed in rats a weak antagonism of a competitive nature. Vitamin A excess in lambs had no effect on serum calcium but lowered serum inorganic phosphorus.