ANNUAL REPORT, 1931 209 



Cranberry Photosynthesis Studies. (H. J. Franklin in cooperation with 

 the Bureau of Plant Industry, U. S. D. A.). This line of stud}^ was pursued very 

 intensively during the summer seasons of 1930 and 1931 by Dr. William H. 

 Sawyer of Bates College, given summer employment especially on this work, 

 and Dr. H. F. Bergman of the Bureau. The results of their work are now being 

 prepared for publication. A summary of their findings for 1930 and 1931 follows: 



1. The climax of photosynthetic activity is reached by the middle of the 

 forenoon (on a clear day), and the sugar content of leaves falls off after midday. 

 This cycle of activity seems to be somewhat correlated with stomatal behavior, 

 for in general there is a tendency for the stomata to close by noon, particularly 

 if the temperature is high. It should be noted, however, that behavior of the 

 stomata is exceedingly erratic, and the stomata do not all open or close at the 

 same time, even in the same leaf. 



2. The curve of sugar production in both the Early Black and the Howes 

 varieties is subject to wide fluctuations on different days, even under apparently 

 similar conditions of light and temperature. These fluctuations are in part cor- 

 related with the amount of sugar already present in the leaves; i.e., the gain in 

 sugar is more rapid after a cloudy day when the sugar content is low than when 

 the leaves start their photosynthetic activity with a sugar content already high. 



3. Increase or decrease of reducing and total sugars usually, but not always, 

 corresponds on a given day. 



4. The percentage of reducing and total sugars in proportion to the weight 

 of the leaves is consistently higher throughout the season in both young and 

 old leaves in the Early Black than in the Howes variety. 



5. An average of sugar production over several consecutive days infiicates 

 that, while the amount of sugar relative to the weight of the leaves is higher 

 in the Early Black than in the Howes variety, the net amount produced over a 

 given period does not differ appreciably in the two varieties. 



6. Beginning with the middle of August there is a marked reduction in the 

 amount of sugar present in both young and old leaves of both varieties. More- 

 over, it would appear that the withdrawal of sugar from the leaves, in comparison 

 with its formation, is greater than earlier in the summer; and except under the 

 most favorable conditions the withdrawal of sugar exceeds its formation. 



7. The proportion of reducing sugars to total sugars in the leaves is less in 

 the latter half of August than earlier in the season. 



8. In mid-season starch is present in cranberry leaves in an amount roughly 

 proportional to the maturity of the leaf. Little or no starch occurs in the rosette 

 of young leaves at the top of the upright, but the amount increases progressively 

 downward, including the old leaves. By the first of August, however, the starch 

 stored in the old leaves begins to be withdrawn, leaving the upper layer of pal- 

 isade cells first. Old leaves, by the time they turn 3'ellow and fall, are devoid of 

 starch. 



9. During cloudy weather, or when the plants are kept in the dark, starch 

 is removed first from young leaves near the top of the upright. A week in total 

 darkness does not appreciably lower the starch content in the old leaves (leaves 

 of the previous year's growth) in mid-June, but all starch is removed from leaves 

 of the current season by such treatment. 



10. In leaves of corresponding maturity there is usually more starch in 

 those of the Early Black than in those of the Howes variety. 



11. In stems, the starch in uprights is restricted to the pith; the starch in 

 runners appears in the pith, wood rays, wood parenchyma, and outer cortex. 

 The older portions of the stem contain most starch. 



