12 



THE CELL 



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which is termed protoplasmic rotation or circulation.* This is not the 

 place bo consider in detail either the external features of the different 

 tonus of protoplasmic streaming or the internal causes of this pheno- 

 menon, since these matters pertain to the field of pure physiology. 

 Brief reference must, however, he made to a circumstance which was 



first clearly pointed out by de Vries, namely, the 

 fact that these movements of the protoplasm 

 greatly facilitate intracellular translocation and 

 metabolism in general. Rotation and circulation 

 of the protoplasm enable substances which enter 

 the cell to distribute themselves and to inter- 

 mingle with comparative rapidity, whereas these 

 processes would take place very slowly if they 

 were entirely dependent upon diffusion. The 

 rapid intermixture effected in this manner in its 

 turn appreciably accelerates the transference of 

 material from cell to cell. According to Bierberg, 

 potassium nitrate, lithium carbonate, and thallium 

 sulphate all travel, in the leaves of Elodea and 

 Vallisneria, by means of protoplasmic streaming, 

 at three or four times the rate that could be 

 maintained by diffusion alone. The importance 

 of protoplasmic movement in this respect-must 

 not be underestimated upon the ground that 

 mechanical intermixture can be affected also in 

 various other ways. On the other hand, proto- 

 plasmic streaming is not so general a pheno- 

 menon as de Vries is inclined to suppose; in 

 many instances, indeed, it takes place only as a 

 result of injury, in which case the cells imme- 

 diately adjoining the wound display the most 

 active movement. The streaming which is thus 

 induced or accelerated by traumatic stimulation 

 undoubtedly serves to expedite those metabolic 

 processes which tend to bring about the healing of 

 the wound with the smallest possible loss of time. 

 The course followed by protoplasmic currents of rotation or cir- 

 culation on the whole bears out the notion that the movement serves 

 to accelerate translocation. In an elongated cell, for example, the 

 current usually flows in a direction parallel to the longitudinal axis 

 ot the element. 



When it is therefore considered that in the case of a sporangio- 

 phore of Phycomrjces the streaming protoplasm can travel all the way 



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tip 



Fig. 1. 



Single coll of a hair from 

 a staminal filament of Tra- 

 t.itin virginica. The cy- 

 toplasm consists of a peri- 

 pheral layer, together with 

 a number of protoplasmic 

 strands traversing the sap- 

 cavity. The nucleus lies near 

 the distal end of the cell 

 X400. After Kiihnc. 



