64 SCIENCE PROGRESS 



It is thus seen that such extremes in the external condi- 

 tions are anything but rare, and naturally many questions 

 arise regarding the responses made by the plant. 



There is no gainsaying the fact that salt-marsh plants 

 grow and flourish in a soil the salinity of which, and therefore 

 also the osmotic pressure, is continually altering. On theo- 

 retical grounds it consequently follows that the osmotic pro- 

 perties of the absorbing organs, the root-hairs for instance, 

 must also be continually fluctuating. If this were not so the 

 concentration of the soil-water would eventually withdraw 

 water from the plant, which would therefore die if the condi- 

 tions were continued for any length of time. On the other 

 hand, if the salinity of the soil-water decreased, the root-hairs 

 would absorb large quantities of water, more possibly than the 

 plant could get rid of by transpiration, so that the internal 

 hydrostatic pressure would become too great for the well- 

 being of the plant. 



But conclusions based on theory are not always borne out 

 by the observed facts ; it is, therefore, desirable to examine 

 the plants under these varying conditions of growth. 



Before passing on to the observations made at Erquy, brief 

 mention may be made of the work of others in this particular 

 connection. 



Janse * found that if Chcetomorpha were placed in water 

 of a higher degree of salinity than that to which it was accus- 

 tomed, the cells became plasmolysed, but after a longer immer- 

 sion they recovered their normal state. These facts indicate 

 that there had been a readjustment of the osmotic powers of 

 the cells in response to the increased external salinity. 



Nathansohn 2 found, in the case of Codium tomentosum, 

 that the cells were permeable to chlorides, and if a plant which 

 had been growing in a saline solution were placed in fresh water 

 free from chlorides, these salts would diffuse out of the cells 

 until their concentration were the same both within and with- 

 out the plant. Further, the reverse would take place if the 

 plant were removed from one solution and placed in another 

 having a concentration of chlorides greater than the cell-sap. 

 In other words, there was a constant passage of chlorides from 

 the plant to the surrounding liquid, and vice versa until the 



1 Janse, Bot. Centrbl. 32, 21, 1887. 



' Nathansohn, Ber. deut. Bot. Gesells. 19, 509, 1901. 



