TRANSACTIONS OF SECTION K. 785 



TUESDAY, SEPTEMBER 6. 



The following Papers were read : — 



1. The Paths of Translocation of Sugars from Green Leaves. 

 By S. Mangham, B.A. 



The primary object of this research, undertaken at the suggestion of Mr. A. G. 

 Tansley, is the reinvestigation of the paths taken by the sugars during the 

 translocation from the leaves of green plants. Haberlandt, 1 from anatomical 

 considerations, and Schimper, 2 from the results of microchemical investigations, 

 concluded that the sugars travel in the parenchymatous bundle sheaths of the 

 leaf veins — the ' conducting sheaths..' Czapek, 3 however, put forward the theory 

 that while diffusion goes on in all living parenchymatous cells, yet for compara- 

 tively rapid translocation over long distances the sieve tubes furnish the sole 

 paths for the assimilates as a whole. Haberlandt 1 considered Czapek's evidence 

 insufficient to warrant his conclusions, and attached greater importance to 

 fechimper's experiments. 



Both Czapek and Schimper employed Fehling's solution as a test for reducing 

 sugars, a method open to the objections that the reagent is reduced by organic 

 substances other than sugars present in the plant, that a gcod deal of diffusion 

 of cell contents goes on in the hot aqueous solution, and that the small granules of 

 copper oxide precipitated are not always easy to observe. 



A very much better sugar tcet is to be found in the precipitation of yellow 

 osazones in the manner introduced by Senft. 5 Using this method I have secured 

 photomicrographs showing the distribution of osazones after the tissues had been 

 subjected to known experimental conditions. Long longitudinal sections of veins, 

 cut and examined after darkening leaves for suitable periods, showed the distal 

 ends free from osazones. Further down these appeared, as soon in the sieve 

 tubes as in the surrounding parenchyma, while near the base the sieve tubes stood 

 out clearly, on account of the abundance of the contained osazones. Experi- 

 ments with pure sugar solutions have shown that to some extent it is possible to 

 distinguish between sugars, and the method is accordingly being used to study 

 the changes undergone by carbohydrates in darkness. 



The results so far obtained indicate (1) that the sieve tubes provide the main 

 paths for the removal of free sugars from the lamina, and (2) that both monoses 

 and bioses travel in the sieve tubes. 



Some results suggest that there is a periodicity in the translocation of free 

 sugars, and this point is undergoing further investigation. The work is in course 

 of extension to the gymnosperms and lower vascular plants, and it is hoped later 

 on to examine the sieve tubes of some of the larger algre by means of the same 

 sugar test. 



2. Assimilation and Translocation under Natural Conditions. 

 By D. Thoday, M.A. 



Detached leaves of Helianthus animus in very bright diffuse light were found 

 to increase in dry weight at the comparatively low rate of 6 rag. per square 

 decim. per hour, whereas in bright sunshine, even under a canvas screen, the 

 rate previously observed had been 17 mg. 



Attached leaves showed a smaller rate of increase than detached leaves, 

 but the difference was less in diffuse light than in sunshine, and in dull light 

 practically nil. The full explanation of these facts is still to be sought, but 

 translocation is probably the prime factor concerned : in one experiment a 

 detached leaf which was rather limp increased in dry weight as rapidlv as 

 attached leaves, which gave readings with the horn hygroscope three or four 

 timee as high. 



1 Pringsh. Jahrb., 1882. 



2 Bot. Zeit., 1885. 



: ' Sitz. Akad: Wien, 1897. " """ 



4 Physiologische Pflanzenanatomie, 1904, p. 3"0. 



6 Sitz. Ahad. Wien, 1904. 



