THE METHOD OF MOVEMENT 185 



single narrow strand. Under such conditions a single 

 rotating or streaming unit may be a decimeter or more 

 long. This would necessitate less frequent diffusion across 

 walls. 



h. Another major weakness in this streaming hypothesis 

 is that streaming has not been demonstrated in mature 

 sieve tubes, except in such aquatics as Elodea, and in these 

 the cells may not be typical or true sieve tubes. The facts 

 that active streaming and rotational movements have 

 been observed in practically all types of living plant cells, 

 that this is especially noticeable in elongated cells, and 

 that a not unreasonable explanation for failure to observe 

 streaming in mature sieve tubes is at hand, as explained on 

 page 174, all greatly reduce the seriousness of this weakness. 



c. Tests with aquatic plants, like Elodea and Vallisneria 

 which show active streaming, have not clearly demon- 

 strated that streaming, even when it is known to take 

 place, is effective in greatly hastening transport. Bierberg 

 (1908) observed that transport was faster in plants showing 

 protoplasmic rotation than in those in which streaming 

 was stopped by ether. The increased rates, however, were 

 only between three and four times those in the check plants 

 and this seems rather insignificant. Although Bierberg 

 states that he used potassium nitrate, sodium chloride, and 

 lithium carbonate, he does not state which of these gave 

 the reported results. Kok (1931, 1933), using pieces of 

 Vallisneria leaves and Drosera tentacles, tested the influence 

 of protoplasmic rotation on the transport of Uthium nitrate 

 and caffein. She was unable to detect any accelerating 

 influence of rotation on transport, although both the 

 reagents penetrated into the vacuoles. 



A failure to demonstrate an accelerating influence of 

 rotation on the transport of Uthium salts or caffein is not 

 conclusive proof that such streaming will not favor trans- 

 port of other solutes. It is probable that Hthium is not 

 taken up by the streaming part of the system. Birch- 

 Hirschfeld was unable to demonstrate transport of lithium 

 through the phloem, yet it has been conclusively demon- 



