RELATION OF AGE AND OF SEASONAL CONDITIONS TO COMPOSITION OF ROOT, PETIOLE, AND LEAF BLADE IN RHUBARB

Abstract

The chemical changes occurring during the season''s growth in roots, petioles and leaf blades of the rhubarb plant were studied in samples taken at four intervals during the season. Total solids reached a maximum in the leaf blade when they were emerging from the soil, decreased rapidly during the growth of the leaf and reached a stationary value after growth ceased. The leaf mesophyll and petiole were practically free from starch at all ages. There was no evidence of a concentration gradient in sugars such as to indicate the transportation of sugars from the leaf through the petiole. In some cases titratable acidity calculated as malic acid accounted for 18 to 25% of the dry weight of the petiole. Nitrate nitrogen was present in small amounts in the young leaves and increased considerably as the leaves became older. The petioles increased in nitrate N with age to as high as 1.53% of the dry weight.