THE METHOD OF MOVEMENT 207 



Schumacher suggests that movement through sieve 

 tubes takes place in the protoplasm and not in the vacuole 

 or the walls, but that it is not carried by moving proto- 

 plasm. His chief reasons for thinking that moving proto- 

 plasm is not concerned are that the rate of movement is 

 much faster than that observed in ordinary parenchyma 

 cells and that the sieve tubes did not show one-sided 

 staining, which would point to a returning, unstained 

 stream of protoplasm. The first objection is not neces- 

 sarily very serious. His data indicate that, under optimum 

 conditions, the dye moved through the sieve tubes at 

 rates running up to 5 or 6 mm. a minute. It is true that 

 streaming in ordinary parenchyma cells and hair cells is 

 nearer one-tenth of this rate, but as is pointed out in 

 paragraph a of Sec. 34, streaming rates of 5 to 6 mm. a 

 minute have been observed in certain much elongated 

 cells, and it is conceivable that the specialized sieve tube 

 may have equal or even greater rates of movement. 



The second objection also is not very serious, for, even 

 in glandular cells where moving strands of fluorescent 

 protoplasm were observed, he found no indication that 

 advancing strands were more deeply stained than others. 

 He found that each cell, as the staining progressed, showed 

 first a fluorescence in the nucleus, and then the protoplasm 

 along the walls showed a gradually increasing light. Even 

 in long cells there was no visible difference between the 

 intensity at the two ends, which he suggests is due to a very 

 rapid spreading of the dye after entrance. Of course, this 

 gradual increase in intensity may have been due to a 

 rapid spread of slowly entering dye along the protoplasm 

 independently of the movement of the latter, or it may 

 have been due to a rapid lateral redistribution from one 

 strand to another by diffusion. Over such short distances 

 diffusion across from one strand to another might be 

 faster than movement of a part of the strand itself from 

 one end of the cell to another. The entrance of the dye 

 may have been so slow that the protoplasm could make a 

 complete circuit before enough entered to develop distinct 



