182 TRANSLOCATION IN PLANTS 



number of plants, and at 25°C. rates of 0.5 to 0.6 mm. per 

 minute in the stamen hairs of Zebrina. Rotational stream- 

 ing in elongated cells of Elodea, Nitella, Chara, Valisneria, 

 and the like, however, has been observed to take place 

 at rates commonly running up to 1 to 2 mm. a minute. 

 Ewart (1903) reports a maximum rate of 6 mm. a minute 

 in Nitella at 40°C. and Lambers (1926) reports maximum 

 rates of 5.5 to 7.9 mm. a minute in Chara, Nitella, and 

 Tolypella at temperatures between 30 and 40°C. 



Although rates of visible protoplasmic streaming in 

 stamen hairs, leaf hairs, ordinary parenchyma cells, and 

 phloem parenchyma cells are usually slower than those 

 observable in large, greatly elongated cells like the inter- 

 nodal cells of Nitella and Chara, it is possible that the 

 streaming in the specialized sieve tubes is as rapid as or even 

 more rapid than the latter. In observing streaming of 

 protoplasm in the leaf cells of Elodea, one can often see 

 that the more elongated cells near the midrib show a more 

 active streaming than the other cells. This strongly 

 suggests that increased streaming activity is associated 

 with increased length of cell units and increased transloca- 

 tion requirements. 



In plants like Nitella there seems to be much less struc- 

 tural organization into fine moving strands than is evident 

 in other parenchyma cells, but even here there is not a 

 general unorganized rotational flow of the contents. I 

 have repeatedly observed differences in rates of movement 

 of particles of different size in Nitella, the small particles 

 moving appreciably faster than the larger ones. As the 

 size of the particles approaches the lower limits of visibility, 

 rates about twice those of the larger particles are evident. 

 Similar more rapid movement of the finer particles in 

 Elodea is also apparent. As Scarth (1927) has pointed 

 out, what appears to be a revolution of the whole cytoplasm 

 in Elodea really consists of a series of separately moving 

 strands of kinoplasm carrying the chloroplasts. It is 

 possible that certain invisible layers of this kinoplasm 

 move much more rapidly even than the finer granules 



