136 The Structure of Protoplasm 



dependence of this activity upon sol ^ gel reactions. In this case 

 it has been found that the rate of streaming diminishes^*^ in propor- 

 tion to the degree of solation which increasing pressure induces in 

 the nonflowing parts of the protoplasm (Fig. 2) . 

 (1) The velocity of streaming in relation to pressure 



Qualitative observations on the rate of streaming as a function 

 pressure are relatively easy to make. At 2,400 Ibs./in.,^ the velocity 

 appears to be about half the atmospheric rate. At 5,500 lbs., the 

 chloroplasts continue to move, but the progress is almost imper- 

 ceptible. Between 6,500 and 7,500 lbs., depending upon the particular 

 cell which is being watched, streaming ceases altogether. However, 

 the flow begins again within about 1 minute after decompression, 

 provided the exposure in the higher range was not too prolonged. 

 In view of such a prompt reversal of the pressure effect, it is not 

 difficult to understand why Fontaine ('29) reported that pressures 

 up to 10,000 Ibs./in.- had no immediate effect upon the velocity of 

 streaming, since this worker was unable to see the cells until a few 

 minutes after decompression had occurred. 



Quantitative measurements of the rate of streaming are some- 

 what difficult to obtain. It is necessary to select a cell which can be 

 brought into sharp focus in the pressure chamber, and with a stop 

 watch to time at least ten individual chloroplasts as they pass 

 through a complete circuit, or at least through a definitely fixed 

 major part of the circuit. Although considerable variation is found 

 from cell to cell, the same cell frequently maintains its individual 

 rate, calculated from the average of ten successive timings, for a 

 period of more than half an hour, provided that the hght and tem- 

 perature conditions are kept constant. In such cells it is possible 

 to measure the pressure rate relative to the initial atmospheric rate. 

 In each case the measurements were discarded if, after decompres- 

 sion, the particular cell failed to return, within 5 per cent, to its 

 original atmospheric rate of streaming. 

 (2) Measurement of the solation effect 



The very marked solating effect of pressure upon the protoplasm 

 of Elodea cells is demonstrated in Figure 4. Leaf A (at 6,000 

 Ibs./in.-) and Leaf B (at atmospheric pressure) were centrifuged in 

 the same field for only 45 seconds. The greater resistance to the 

 displacement of the chloroplasts in the gelated protoplasm of the 

 atmospheric specimen is indicated by the absence of any clear sedi- 

 mentation zones. Such clear sedimentation zones may be obtained 



