759 



sap, clearly show how the osmotic value of the leaf-cells increases 

 with the possibility of assimilation. 



Now I endeavoured to determine the suction force by Ursprung's ') 

 method but the subject appeared to be difficult to experiment on. 



A quantitative determination gave in the green leaves of Aesculus 

 an amount of reducing sugars of 3 7» ")i in the variegated (yellow) 

 leaves I 7o. i" t''^ ringed variegated (yellow) branches only traces. 

 In general also the amount of extractable salts is trifling; in green 

 and variegated leaves 0,9 7. of the fresh weight '). Sprecher finds 

 in yellow varieties lower osmotic values for the cell sap than in 

 the green specimens*). 



True, the variegated leaves of the ringed branches of Aesculus 

 contain from 18 to 20 7u protein and 5 7, dextrin (calculated at 

 dry weight) but the influence of these amounts on the osmotic pres- 

 sure is nothing to speak of. Yet this does not explain all, for in 

 the variegated completely ringed shoots wood and hark above the 

 ringing appeared to contain still a fair amount of starch (6 7, of 

 the dry weight, against 9 "/„ in the partially ringed branch), while 

 the leaves were already shrivelling. 



Why this starch is not converted into sugar and why, when 

 transported to the leaves, it does not raise the osmotic pressure has 

 not yet been explained. 



However this may be, the partially ringed variegated branches do 

 not die ofJ'. It appears, then, that there the supply is not cut off 

 and that consequently the young parts are provided with the nutri- 

 ment that in the green ringed branches is produced by assimilation. 



According to Hanstein the organic products are conveyed along 

 the bridge of bark, but if this is the case, we must relinquish Hartig's 

 hypothesis that the transport is effected along the xylem while the 

 branches are budding. 



Otis Curtis (I.e.) does so and was led by his ringing experiments 

 to regard the phloem exclusively as the path, along which the saps 



'l Ursprung, Ber. d. d. bol. Ges., 1918. 



°) Strictly speaking 2 "/n and 1 "/n reducing sugars derived from glucosids 

 (calculated at dry-weight). 



') The starcli determination.s were performed by putting the pulverized material 

 immersed in water for 3 liouis into an autoclave at 4 aim., and by subsequently 

 boiling the aequeous extract with diluted hydrochloric acid during 60 minutes. 



Plasmolytic experiments are objectionable on account of the osmotic pressure 

 in the various cells being unequal. Still, a 10% saccharose solution plasmolyzes 

 the variegated Aesculusleaves, not however the green ones. 



*l A. Sprecheh. Rev. Gen. Bot. 1921. 



