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SCIENCE PROGRESS 



the stronger veins ; this, slowly diffusing through the cells, 

 gives Schimper's results in the larger veins. 



Schimper's work on laticiferous tubes has already been 

 referred to, but it will here be well to indicate his general 

 line of argument. He considered that if the laticiferous tubes 

 serve to remove carbohydrates from leaves in the same way 



Fig. 19.— Diagrammatic representation of the distribution of sugar in a leaf 

 which has been in darkness for some time. 



The concentration of the sugars is indicated by dots, while arrows show the direction of motion. Only 

 the spongy niesophyli, bundle sheaths and the phloem of the vascular bundles are represented. 



as he supposed the bundle sheaths to do, then certain things 

 should hold good. In the first place the carbohydrates present 

 in the latex under ordinary conditions must rapidly disappear 

 on darkening the plant; secondly there must be a definite 

 relation of the assimilatory cells to the laticiferous tubes, such 

 as had been described by Haberlandt; and thirdly the carbo- 

 hydrates formed in the mesophyll must travel towards the 

 laticiferous tubes just as they do towards the bundle sheaths. 



