Titration Curves of Etiolated and of Green Wheat Seedlings Reproduced with Buffer Mixtures.

Introduction Trhe titration curve for the expressed juice of etiolated wheat seedlings has a pronounced inflection above pH 8.0 (fig. 4), which does not occur in the curve for fully green seedlings (fig. 5). An intermediate type of curve, linear between p1I 8.5 and 11.0, is characteristic of very young seedlings just after their emergence from the ground. when, from the standpoint of chemical composition. they are partially etiolated (fig. 6). The characteristic inflection in the etiolated-seedling curve seemed due to some buffer present in maximum concentration in the absence of chlorophyll, and the change in the form of the curve during the period of seedling developinent appeared to be caused by a progressive diminution in the amount of this buffer as assimilation processes became established. The object of the present investigation was to identify this buffer, and to determine whether the titration curves of etiolated and of green wheat seedlings could be reproduced by varying its concentration in chemical mixtures containing it in combination with other buffer compounds known to occur in plant juices. Material The etiolated seedlings from which juice was obtained for the representative titration curve in fig. 4 were of the variety White Odessa, grown in the darkness in pure wA-hite sand without nutrients at a temperature of 180 C. The plants were eight days old and about 8 cm. high at the time of cutting, with the first leaf just emerging from the coleoptile. The green seedlings, from which the juice was obtained for the representative titration curve in fig. 5, were of the same variety, grown in soil under normal greenhouse conditions, at approximately the same temperature. The plants were cut eight days after their emergence from the soil. They were 8-10 cm. tall, with one fully expanded leaf. The characteristic inflection in the etiolated-seedling curve was the same for seedlings grown in soil, pure sand, and on saturated blotting paper without nutrients. The curve for fully green seedlings never showed this inflection whether the plants were germinated in soil or in pure sand without nutrients. The form of the green-seedling curve varies with age,-from the type suggesting partial etiolation, characteristic of emergent seedlings, to that 307