Protoplasmic Streaming — Relation to Gel Structure 135 



6,000 lbs. no pseudopodia can be formed or maintained, and the 

 Amoebae become completely spherical. With few exceptions the 

 equilibrium form is assumed by all of the specimens of an experi- 

 mental group, whether the particular pressure is approached from 

 a higher or a lower level. Apparently each characteristic form 

 represents a steady state with respect to the conditions imposed by 

 the pressure. 



The extent to which the variations in the diameter of the pseudo- 

 podia may be accounted for on the basis of the increased fluidity of 

 the plasmagel constitutes an interesting question. Essentially, a 

 pseudopodium must be a tube of plasmagel through which the plas- 

 masol flows outward as extension is occurring, and the tubular form 

 of a pseudopodium must be maintained by rigid properties residual 

 in the plasmagel wall. Due to the solating effect of an increase of 

 pressure, a gel layer of equal thickness would possess a lesser 

 strength. On the basis that hydrodynamic factors are involved in 

 the flow of plasmasol, a reduction in the diameter of the pseudo- 

 podium can be regarded as a compensation for the diminished 

 strength of the wall. The situation would be analogous to a tube of 

 smaller diameter successfully conducting a fluid which is flowing 

 under a pressure that would be sufficient to rupture the wall if the 

 diameter of the lumen were greater. 



Some further observations appear to justify the foregoing view- 

 point. At pressures below 3,000 lbs., a range in which an appreciable 

 protoplasmic flow continues, a few of the pseudopodia do not extend 

 steadily in one direction. Instead, the progress of the extending 

 pseudopodium is interrupted at intervals of about 15 seconds by 

 sudden ruptures in the lateral wall, just proximal to the advancing 

 tip. When a rupture occurs, the protoplasmic granules pour rapidly 

 out into the resulting lateral bulge, and then the flow stops altogether 

 for a moment. When the advance begins again, the direction is 

 deflected slightly toward the ruptured side. Such pseudopodia 

 assume a somewhat tortuous form. It would seem probable that this 

 phenomenon indicates an incomplete compensation in the particular 

 pseudopodia which are involved, and that the diameter of these 

 pseudopodia is reduced to a degree which is not quite sufficient to 

 provide stability during periods of active flow. 



B. CYCLOSIS 



A study of the effects of pressure upon protoplasmic streaming 

 in the leaf cells of Elodea (Marsland, '39b) , has also established a 



