THE PHYSICAL PROPERTIES OF CYTOPLASM 75 



This is doubtless due to the fact that cj'toplasm is a complex sol composed 

 of many different proteins, each one of which may possess an isoelectric point 

 different from that of the others. Measurements of the cytoplasm of cells 

 in the root tips of different plants showed the isoelectric range to be from; 

 pH 4.6 to pH 5.0 (Naylor, 1926). These values appear to be representative 

 for cytoplasm in general. 



Cytoplasm is usually on the alkaline side of its isoelectric range (see later 

 discussion of the pH of the cytoplasm) and therefore we would expect to 

 find that its constituent micelles are negatively charged. That this is true at 

 least for the visible granules of the cytoplasm has been shown by Sen (1934). 

 Cataphoretic migration of the granules in the cytoplasm of root hair cells and 

 epidermal cells toward the anode was shown to occur, thus indicating that 

 these particles carry a negative charge. 



The proteins present in the nucleus apparently possess different isoelectric 

 points from those of the cytoplasm. Furthermore, it is probable that some 

 portions of the cytoplasm possess isoelectric points different from those of 

 other parts of the cytoplasm in the same cell. 



Cytoplasm contains dissolved electrolytes and would therefore be expected 

 to conduct an electrical current. Brooks (1925) determined the electrical 

 conductivity of the plasmodium of the myxomycete Biefeldia maxima and 

 found it to be equivalent to that of a O.OO145 N solution of NaCl, which is 

 a relatively low value. The solution in the moss substrate on which the 

 Plasmodium was growing had a conductivity only about one-third as great as 

 that of the plasmodium. Evidence was also found that the conductivity of 

 the protoplasm varies according to the conductivity of the medium with which 

 the cells are in contact. 



8. Streaming. — In many cells the cytoplasm may be seen in active move- 

 ment. In the simplest cases this movement consists of a rotation of the cyto- 

 plasm around the inner surface of the cell wall. Where cytoplasmic strands 

 extend through the vacuole as in the case of cells of Tradescantia stamen 

 hairs the circulation of the cytoplasm may become very complex. The fluid- 

 like portion that is in motion is often bounded by thin layers of non-moving 

 cytoplasm. The cytoplasm immediately adjacent to the cell wall and that 

 which bounds the vacuole often does not move. The plastids and the visible 

 granules are carried passively around the cell by the moving cytoplasm. The 

 causes of cytoplasmic streaming {cyclosis) are unknown. It is accelerated by 

 increases in temperature up to the point where injury appears and checked by 

 low temperatures, ceasing at temperatures slightly above the freezing point. 

 Cj'closis is also stopped in the absence of oxygen and by anaesthetics in rela- 

 tively high concentrations. In dilute concentrations toxic substances such as 



