Protoplasmic Streaming — Relation to Gel Structure 155 



activities, the group in which protoplasmic streaming constitutes 

 the common attribute. 



C. POSSIBLE MECHANISMS BY WHICH GELATION MAY PRODUCE STREAMING 



(1) VoliLme changes in relation to streaming 



In an earher paper (Marsland and Brown, '36) it was suggested 

 that the motive force of streaming in the amoeboid cell might take 

 origin in the small changes of volume which occur during the gelation 

 and solation of the cytoplasm. This position now seems untenable in 

 the light of Heyman's ('35 and '36) work. In all probability the sign 

 of these changes is in reverse, that is to say, just the opposite kind 

 of volume changes would be necessary to give streaming in the 

 proper direction. The decrements of volume would need to occur 

 anteriorly, near the tip of the pseudopodium, where gelation is 

 known to be taking place, and the increments of volume would need 

 to be localized posteriorly where solation is occurring. To provide 

 volume changes of the proper sign, the plasmagel of the Amoeba 

 would of necessity belong to Freundlich's type II, but in this case 

 one would expect to obtain gelational effects from pressure, instead 

 of the solation which has clearly been demonstrated. 



In the streaming of plant cells, however, the possibility still 

 remains that volume changes accompanying a series of sol ^ gel 

 reactions play an important role in generating the motive force 

 (Marsland, '39b) , but the question cannot be answered decisively 

 until the focal points where solation and gelation take place have 

 been localized more definitely. The high turgor which is character- 

 istic of the plant cell provides a favorable condition for the effective- 

 ness of such changes, since a greater fund of energy is mobilized 

 when volume changes take place in a medium under the constraint 

 of higher pressure. 

 (2) Contractile theories of streaming 



According to Lewis ('39) streaming in amoeboid cells"- and the 

 movements which occur in dividing cells are motivated by elastic 

 and contractile properties which are inherent in gel structures gen- 

 erally, and in the plasmagel systems of certain cells in particular. 

 Given time, most gels do, of course, undergo a process of contraction 

 by which gradually the sol is squeezed forth from the colloidal 

 interstices into the surrounding medium, as, for example, serum is 

 expressed from a blood clot, or soap solution from a soap gel. 



Such a theory presupposes, no doubt, that shrinkage in the 



