308 Tin' Carho/n/(h'afes of the Jfonfjohf Leaf 



diffusion of the reducing sugars would be four times that of the cane 

 sugar; moreover, as was emphasised by Brasse [1886], if the storage of 

 cane sugar is accompHshed by a direct wandering of this sugar as such 

 from the leaf to the root, it would be in direct defiance of the ordinary 

 laws of tlifi'usion, as motion would occur from a place of low concentration 

 to one of high concentration. If, however, the sugar is translocated as 

 hexose and is immediately transfoniied in the root into saccharose, 

 these objections no longer hold and a continuous stream of sugar could 

 be maintained. It is probable, too. that the actual mechanism adopted 

 serves to keep the cane sugar, once it is formed in the root, from getting 

 out; de Vries' [1879J well-known experiment may be recalled, in which 

 he showed that strips of beet-root could be soaked in water for 14 days 

 without the presence of sugar being detected in the surrounding 

 water. Gutzeit [1911] has also recently emphasised the impermeability 

 to saccharose of the protoplasm of the.cell- walls of the beet-root, pointing 

 out that in the ordinary process of manufacture of sugar from the 

 beet it is necessary to use Jiot water first, to kill the protoplasm, before 

 the sugar can be extracted. Brasse [1886] showed that the same 

 effect could be produced by chloroform. If the protoplasm is permeable 

 to the hexoses and not to the saccharose a simple mechanism would 

 exist by which the root could store up sugar without any possibility of 

 loss by back-diffusion, and an explanation would be given of the fact 

 that although the concentration of sugar in the root may be diminished 

 after heavy rains by the inflow of water, the actual total qmintity of sugar 

 in the root steadily increases throughout the season's growth and never 

 shows any falling off (Vivien [1913]). It has been generally assumed 

 that, in the second year's growth of the beet, when the cane sugar is 

 utilised to form new shoots, the saccharose is first inverted by in- 

 vertase in the root and is conveyed in the form of invert sugar to 

 the growing points. But according to Cohn [1915] invertase is not 

 found in the root even in the second period of growth, when the seed- 

 bearing plant is beginning to form ; the saccharose is held to undergo 

 inversion in the stalks and leaves of the new plant. 



It still remains to consider the means by which the hexoses wiiicii 

 are carried into the root are transformed into saccharose. The 

 complete absence of invertase from the root mihtates against the view 

 adopted by Robertson, Irvine and Dobson [1909] that the cane sugar 

 is formed by a process of reversible zymo-hydrolysis, in which the 

 invertase acts as a synthetic agent. These authors recognised this 

 difficulty and were driven to assume that saccharose is formed, not 



