. Adventures in radioisotope research;. Radioactive tracers; Radiobiology. 888 ADVENTURES IN RADIOISOTOPE RESEARCH (b) the phosphorus atoms migrate. In case (a) labelled phosphorus atoms should only be found in the upper leaves; in case (b) the labelled phos- phorus atoms should be equally distributed between the upper and lower leaves. As is seen from Table 1, the lower leaves contain an appreciable amount of labelled phosphorus atoms, clearly showing that in the case of the sunflower, just as in that of the maize plant, a very considerable migration of the phosphorus atoms takes place, and t
. Adventures in radioisotope research;. Radioactive tracers; Radiobiology. 888 ADVENTURES IN RADIOISOTOPE RESEARCH (b) the phosphorus atoms migrate. In case (a) labelled phosphorus atoms should only be found in the upper leaves; in case (b) the labelled phos- phorus atoms should be equally distributed between the upper and lower leaves. As is seen from Table 1, the lower leaves contain an appreciable amount of labelled phosphorus atoms, clearly showing that in the case of the sunflower, just as in that of the maize plant, a very considerable migration of the phosphorus atoms takes place, and the probability of a labelled phosphorus atom being found in a preformed leaf is not very. 0 days different from the probability of its being found in a leaf grown in a labelled solution. In comparing the figure obtained for the lower and upper leaves, we have to take into account the fact that the lower leaves increase in size to some extent while the plant is in the labelled solution. However, this increase was found to be very slight, as to be seen from the third vertical column of Table 1 and also from Fig. 1, which illustrates the plant at the three different stages of its growth. From the above, it follows that the greater part of the phosphorus atoms are not fixed in position in the leaves but can migrate. The bulk of the phosphorus atoms found in plants are presumably present as inorganic phosphate, and carried about with the circulation stream in the plant. To what extent the phosphorus atoms present in organic combination are permanently localized is under investigation. In connexion with the experiments discussed above, we tried to ascertain if any exchange of phosphorus atoms takes place between an isolated leaf and a nutritive solution. These experiments were carried out with the leaves of a sunflower grown in labelled nutritive solutions. Some of the leaves were ignited and analysed at once after separating them from the stem, while other leaves were placed for 48
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