138 TRANSLOCATION IN PLANTS 



cells, but in older cells, when the protoplasm is limited 

 to a parietal layer, this type of activity ceases. He 

 opposed the views of Sachs and Van Tieghem that the 

 protoplasm is dead and the sieve tubes are merely passive, 

 but he considered that the tubes are physiologically active 

 in the transport of materials, and he thought that, at 

 least in those forms with open pores between the cells, 

 there is a mass movement of albuminous material from 

 one cell to another in one direction. He pictured sieve 

 tubes of several plants showing droplets passing through 

 the pores from one sieve-tube segment to another. He 

 described several as passing toward the base of a plant, 

 but in a young subterranean shoot of Rubus idaeus the 

 position of the globules indicated a movement toward the 

 apex. In a long branch rooted at the tip the position 

 of the globules indicated a movement toward the base 

 of the mother plant in the main part of the branch, but 

 near the tip the direction of movement was toward the 

 newly developing roots. Though he observed streaming 

 in companion cells and young sieve tubes and emphasized 

 the importance of diffusion between cells, he evidently 

 considered that the movement in mature sieve tubes is 

 by mass flow chiefly in one direction, and not of the circu- 

 lation or cyclosis type. He considered that the high 

 turgor in the sieve tubes, changes in temperature, and the 

 removal of translocated material in the growing and 

 storage regions are of importance in favoring rapid diffusion 

 and increased mass movement of these substances. It 

 is worth noting that, in his figures (Figs. 3, 5, 7, Plate 21), 

 which show this mass movement of cell contents through 

 pores, the protoplasm is strongly retracted from the lateral 

 walls of the sieve tube. This would indicate a collapse 

 due to the treatment, which might also easily account 

 for an abnormal squeezing of the contents through the 

 pores. In order to relieve the internal pressures and 

 prevent this flow in some cases he cut and mounted the 

 material in 3 to 5 per cent sugar solutions. Although 

 such treatment may somewhat reduce the rapid flow 



