THE METHOD OF MOVEMENT 137 



be hastened by the presence of sucrose, the main criticism 

 of the inadequacy of diffusion alone is not met. DeVries 

 (1885) presented calculations of Stefan who had estimated 

 that by diffusion alone it would take 319 days for 1 mg. 

 of sodium chloride, one of the most rapidly diffusing 

 salts, to move a distance of 1 m. from a 10 per cent solu- 

 tion. This calculation was based on the assumption of a 

 column of pure water at the beginning into which the salt 

 was diffusing. Similar calculations indicated that for a 

 similar quantity of sugar to diffuse the same distance under 

 similar conditions it would take 2 years and 7 months 

 and for a soluble protein 14 years. Of course, after the 

 solute has established a gradient over the distance and 

 if the concentration is maintained at zero at the meter 

 distance and a steady state of diffusion obtains, then 

 sucrose, according to Fick's law, should pass the plane a 

 meter distant from a 10 per cent solution at the rate of 

 1 mg. in about 10 hr. (595 min.). This, however, is too 

 slow to account for normal solute movement. DeVries 

 observed active streaming, of both the circulation and 

 rotation types, in the companion cells and parenchyma 

 of the phloem of a number of different kinds of plants and 

 suggested that the streaming might account for a much 

 more rapid movement than would occur if restricted to 

 diffusion. Hartig (1858) had previously suggested that 

 the movement of protoplasm which he had observed in 

 living cells might actually be the moving nutritive sap. 

 Velten also (1872) had observed and described streaming 

 in sieve tubes and many other types of living cells. This 

 hypothesis seems to have been largely discarded after a 

 few years when investigators failed in attempts to observe 

 streaming in mature sieve tubes. 



A few years later Lecomte (1889) stated that no problem 

 is more important to the life of the plant than transloca- 

 tion and none has been more neglected by botanists. In 

 explaining the possible mechanism of transport he stated 

 that he had observed streaming of a rotational type, 

 passing from one end of the cell to the other in young 



