68 SCIENCE PROGRESS 



This tendency possibly supplies an explanation of the 

 greater thickness of the cell-walls of the apical region of the 

 root-hairs of Salicornia. 



Further, it was observed that the osmotic pressure of the 

 root-hairs of the same individual plant varied ; generally the 

 younger hairs had a higher equivalent, whilst the cells of the 

 root-cap had a very low co-efficient. Also, a variation in the 

 osmotic strength of the root-hairs of different individuals 

 growing in the same locality was sometimes observed, although 

 this variation was never so great as to cause the internal 

 osmotic pressure to fall below that of the surrounding soil water. 



The next question which naturally arises is, How is this 

 alteration in the osmotic pressure of the root-hairs brought 

 about ? 



Two hypotheses suggest themselves : either the primordial 

 utricle is permeable to salt which passes into or out of the cell 

 according to the differences in pressure on each side of the 

 plasmatic membrane, and so the internal pressure is raised or 

 lowered ; or, chemical changes may take place in the cell, as a 

 consequence of which either a fall or a rise in the osmotic pres- 

 sure would result. 



The work of Nathansohn on Codium, and the fact that the 

 amount of sodium chloride in the seedlings of Salicornia in- 

 creased in amount as the plumule was reached, indicate that 

 the former hypothesis is probable. But on testing the root- 

 hairs for sodium chloride, by means of silver nitrate, no indi- 

 cation of its presence was given. It is, however, possible to 

 explain this negative result. Before testing for chlorides in 

 the root-hairs it was necessary to wash the seedlings in pure 

 water until all adhering chlorides were removed, for, of course, 

 if this were not done the precipitate of silver chloride on the 

 outside of the root-hairs would make it very difficult, if not 

 impossible, to arrive at a satisfactory conclusion regarding the 

 presence or absence of this substance within the hairs. The 

 washing, however, would lower the external osmotic pressure ; 

 consequently, relatively much water would be absorbed and 

 passed on to the more internal tissues, so that the root-hairs 

 would be washed free from salt. Or, from Nathansohn 's work, 

 the salt would pass out of the root-hairs into the surrounding 

 water owing to the difference in the concentration of this sub- 

 stance. 



