Chapter VIII — 127 — Active Relations 



about 96 per cent of the fresh weight. For other materials, he believed 

 that imbibed water in cell walls and protoplasm, released on pressing, 

 could produce deviations much greater than purely methodical errors in 

 technique. Hence, values obtained for several species (Table 41) are, if 



Table 41. — Cryoscopy of sap expressed from several marine algae and of the sur- 

 rounding sea water. Atmospheres at 20° C. {data of Mosebach, 1936) : — 



Expressed 

 Brown alga£ sap Sea water Difference 



Cystosira harbata (shoots) 30.2 



Sargassum linifolium ("leaves") 31.8 



Sargassmn linifolium (swimbladders) . . . 31.7 

 Red algae 



Rytiphlaea tinctora 29.6 



Spyridia filamentosa 29 



anything, too low. This table indicates that the osmotic pressure of these 

 plants varies from 3.8 to 6.7 atm. above that of sea water. This infers that 

 turgor pressures are also in this range of magnitude, but there is no proof 

 that this is so. Valonia macrophysa and V, utricularis show a difference 

 of only about an atmosphere between the surrounding sea water and sap, 

 which can be obtained in an almost pure state. 



Osmotic regulation in these forms must be largely one of accumulation 

 of solutes, mostly salts. Osmotic adaptation by Nitella translucens to 

 changing external concentration has been demonstrated (Wildervanck, 

 1932) ; a much greater regulative capacity is exhibited by many land plants 

 (Gasser, \9A2—see Chapter VII). 



These results were interpreted to mean that imbibitional phenomena 

 must be taken into account in measurements of osmotic pressure of ex- 

 pressed sap, although they do not preclude the possibility that water secre- 

 tion forces may also be present. The differences demonstrated may actu- 

 ally be small compared to those which might obtain in other plants. 



Auxin and Water Uptake : — The storage parenchyma of the tuber of 

 Solanum tuberosum is a favorite experimental object for certain types of 

 water relation studies, since it provides a large amount of homogeneous 

 tissue. Stiles and Jorgensen (1917) observed that the swelling of potato 

 tissue in tap and distilled water did not conform to current ideas of an 

 osmotic system. A temperature coefficient (Qio) of about 3 was indicated. 

 This is not characteristic of purely physical systems, and has been inter- 

 preted by Commoner, Fogel, and Muller (1943) as pointing to an en- 

 zymatic process associated with water absorption. 



Several investigations have been undertaken to demonstrate the effect 

 of auxin on water and salt uptake in potato. While the effect of auxin on 

 growth processes has been a fertile field of research for many years, its 

 role in the water relations of the plant cell has been recognized only re- 

 cently. Reinders (1938) found that potato tuber tissue showed an in- 

 creased water uptake under the influence of auxin. In preliminary experi- 

 ments, tissue discs 1 mm. thick and 17 mm. in diameter were permitted to 

 remain in "stagnant" tap water for 24 hours, then were transferred to 

 aerated distilled water, whereupon a considerable increase in wet weight 

 occurred in the amount of from 18.6 to 30.5 per cent of initial weight after 

 8 days. Slight increases were noted even when the transfer was to non- 



