Abstract. Pinus strobus L. plants in their third year of growth were permitted to photoassimilate '4CO, for about 1 hour at monthly intervals between April and October, and the subsequent distribution of 14C in these plants was determined 8 hours, 1 month, 2 months or 4 months after photo-assimilation. In this way, the fate of 14CO2 photo-assimilated during different months of the growing season was observed.In the spring, old needles played a significant role in photo-assimilating 14CO0 and exporting current photosynthate to the developing new shoots and roots. By July, the new shoot had replaced the old shoot both as the primary photo-assimilating part of the plant and as an exporter, particularly to the root.The root received current photosynthate from the shoot throughout the entire growing season, although plant analysis only 8 hours after photo-assimilation did not always reveal this. Trarnslocation of recent photosynthate from shoot to root was particularly high in August, September, and October.The amounts of photo-astsimilated 14C lost from the plants over a 4 month interval, principally through respiration and photorespiration, were about one-half of that absorbed during photo-assimilation, with the greatest loss occurring within the first month.3 No. 6 ine 1968To gain insight into the sources of carbohydrates for growth of various parts of a tree at different times of the year, studies using defoliation, girdling, and combinations of these techniques (1, 8,9,11,16,17), as well as observations on the contributions of dififerent aged needles (10) 3 Deceased.old shoot, and new shoot. The second objective has been to determine the amouints of 1"C lost from the plants after various periods of time following "CO. photo-a,ssimilation. A third objective has been to observe the partition of retaiined 1"C between the 80 % ethanol-soluible and insoluble fractions.Thi,s study represents an extension of previous work (13,18,19)

Soybean plants (cv. Harosoy 63) inoculated with rhizobia were germinated from seed and beginning on day 7 after planting were subjected to one of four patterns of nutrient fertilization. One group received a nutrient solution containing 5 mM nitrate, a second group received nitrate-free nutrient solution, and two other groups received nitrate-containing solution either from days 7 to 13 or from days 14 to 20. On day 21 rates of leaf photosynthetic CO2 uptake and nitrate reductase activity were measured, as well as the capacities of the leaf to export recent photosynthate and of the nodules to reduce acetylene. The data support the hypothesis that sufficient nitrate availability in the leaves of young soybean plants can modify both photosynthetic CO2 uptake and light-mediated photoassimilate export to an extent that nodule development and the capacity for nitrogen fixation are reduced.

By measuring the number of water molecules per ion moved electroosmotically through living membranes of Nitella flexilis before and after the addition of chemicals to a solution of 10−4 M KCl, the effect of the chemical upon electroosmotic transport was investigated. Carbon tetrachloride and chloroform reduced slightly the amount of water transported per ion. On the other hand 10−5 M indoleacetic acid caused major changes in electroosmotic transport, increasing it in cells tested in July–August, but decreasing it in cells tested in October–November. Different ions also carry different amounts of water with them electroosmotically. These changes can be interpreted in terms of changing pore size.The relative pore size was also determined by measuring the permeation of glucose-14C and sucrose-14C in the absence and presence of electroosmotic transport and in cells treated with indoleacetic acid. Both the plasmalemma and tonoplast were freely permeable to glucose-14C but not to sucrose-14C. However, in the presence of electroosmotic transport sucrose did permeate the cell membrane. Indoleacetic acid enhanced this permeation of sucrose-14C.

In early September after shoot elongation and needle expansion had terminated, pine plants (Pinus strobus L.) in their third year of growth were permitted to photoassimilate 14CO2. At intervals of time ranging from [Formula: see text] to [Formula: see text] months, the distribution of 14C within the plants was determined. Within the first 48 h about 40% of the photoassimilated 14C was lost from the plant through respiration and of the retained 14C, over 50% was found in the root, a value equivalent to about a third of the total 14C activity initially assimilated. Despite continued losses of 14C from the pines, about 30% of the initially assimilated 14C was still present [Formula: see text] months later. Evidence for remobilization of 14C into the following year's shoot growth is also provided.

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