TUKGIDITY 79 



plant be put into a solution without the chlorid, this sub- 

 stance diffuses out of the cells in twelve to twenty-four 

 hours, and the reverse occurs if the external solution con- 

 tains more Cl ions than the internal. Other substances in 

 the medium will cause the retention of chlorid, apparently 

 in inverse proportion to their ability to penetrate. The 

 following table to show this is taken from Nathansohn's 

 paper : 



Medium Pressure 



Normal Sea H 2 O Sw 1 2.25 



Na NO 3 iSw .67 



Na NO 3 Sw 1.27 



Urea Sw 0.64 



Glycerin Sw 1.0 



Grape sugar iSw 1.45 



Of the substances named in the table, those of least pene- 

 trating power are grape sugar and NaNO 3 . This is a new 

 departure, and no definite conclusions can be drawn until 

 more work has been done. 



Very clear evidence of change in permeability of proto- 

 plasm to solutes is that obtained by Haupt 2 in his work on 

 extrafloral nectaries. In certain plants (e. g., Euphorbia 

 and Vicia) he found that the secretion of sugar by the nec- 

 taries was profoundly influenced by light, specifically by the 

 red-yellow rays of the sun's spectrum. Secretion of sugar 

 occurred only in light, and from nectaries already containing 

 sugar this substance was resorbed in darkness or in blue 

 light. This must indicate that the nature of the protoplas- 

 mic membranes here is entirely altered by the etheric vibra- 

 tions; in light sugar passes outward, while in darkness it 

 moves in the opposite direction. That plants which had 



1 Sw in the table denotes the osmotic pressure of normal sea-water. 



2 H. HAUPT, " Zur Secretionsmechanik der extrafloralen Nektarien," Flora, Vol. 

 X (1902), pp. 1-41. 



