Physical Properties of Protoplasm 161 



gel. The whole nuclear substance is quite glutinous. No trace of 

 free liquid could be found in the nucleus. 



SPIROGYRA 



The cellulose wall of Spirogyra is enormously cohesive; it is cut 

 or punctured with extremely fine Jena glass needles with considerable 

 difficulty. The outer surface is covered by an almost invisible soft 

 gel, that frequently measures five or more microns in thickness and 

 can be stained red with sodium alizarin sulphonate in a neutral or 

 slightly alkaline solution. A layer of dilute granular gel covers the 

 inner surface of the cellulose wall and is connected by a number of 

 strands of an elastic gel to a central mass of living substance, in which 

 a small nucleus is imbedded. The central mass of gel contains a 

 few granules and is of a higher viscosity and cohesiveness than the 

 surface cytoplasm. This mass also has a higher refractive index and 

 higher absorptive power than the surface cytoplasm. The anchoring 

 strands of gel decrease in viscosity from within outwards. Much 

 of the surface layer of cytoplasm is usually invisible. Hence, it is 

 quite translucent and has refractive and dispersive powers very close 

 to those of water. If the cell wall be cut across the surface cytoplasm 

 shrinks. The chloroplasts either shrink or separate into rounded 

 masses. The chloroplasts have a higher viscosity and elasticity than 

 the gel in which they are imbedded. 



The pyrenoid is a complex structure. Dissection shows the 

 presence of an optically dense but fragile wall which, when broken, 

 frees a globule that is of considerable interest. This globule shows 

 many of the optical properties of an oil droplet but has too high a 

 viscosity to round up under the influence of surface tension; there- 

 fore it seems to be a true gel. 



None of the cytoplasm goes into solution very readily even when 

 cut into very minute pieces. 



The nucleus of Spirogyra is a gel that has higher viscosity and 

 refractive and absorptive powers than the cytoplasm. It is also 

 more cloudy than the cytoplasm. There are denser areas in the 

 nuclear substance in the form of granules and threads that form a 

 sort of network. Small pieces dissected from all parts of the nucleus 



