Experimental researches on vegetable assimilation and respiration.—XV. The development of photosynthetic activity during germination of different types of seeds

In a previous paper (2) the writer has shown that the photosynthetie activity of the seedling leaves of Phaseolus vulgaris, Vida Faba and Arena sativa is zero or very small for some time after their first appearance, and that oven when further development of chlorophyll is inhibited the activity increases from day to day. Although the photosynthetic activity was measured under such conditions that carbon dioxide was not limiting the rate of assimilation, yet an investigation of the results of growth experiments (3) indicates that under natural conditions of carbon dioxide supply the assimilation of the seedling leaves of maize is very much smaller than that of mature leaves. Tables I, which contains results of experiments carried out by the writer on maize, and la, a collection of scattered results from Willstatter’s work (8), show that some considerable lapse of time is necessary before the seedling leaves of maize attain their full activity, whether light or temperature be limiting; in Willstatter’s experiments temperature was limiting. Experiments recorded by Brenchley (1) show that in the case of Pisum sativum it is some time before the seedling attains a dry weight equal to that of the seed. In the case of Helianthus, however, the evidence from growth experiments (4) indicates that in this plant the seedling leaves, here the cotyledons, assimilate quite actively as soon as they appear above ground, or that at most hardly a day elapses before they reach their full activity. This evidence from growth experiments suggested an investigation of the case of Helianthus on the same lines as that of Phaseolus described in the previous paper. The results of the experiments are recorded in Table II. The same method and apparatus was used as in the previous case (2).