PASSAGE OF WATER FROM PLANT CELL. I O9 



most important part. It has for a long time been suggested that 

 the cells of root tissue possibly act as pumps, forcing water into 

 the vessels, and thus causing root pressure, but whether such 

 expulsion of water in the roots actually occurs has as yet never 

 been satisfactorily demonstrated. Droplets appear on the surface 

 of some mycelial threads when kept in a damp atmosphere, also ^ 

 on many plant hairs and on the rhizomes of Alarchantia under 

 similar conditions. To this list might be added a number of 

 other cases (see Pfeffer's Pflanzen Physiologic). 



Evidence is also gradually accumulating which tends to show 

 that some plants do excrete water at a temperature just above 

 0° C. We have the casual notice of Molisch that in some stamen 

 hairs of Tradcscaiitia subjected to a temperature of — 5° to 



— 9° C. for six hours the plasma membrane separated from the 

 wall, but no freezing took place until a temperature of about 



— 15° C. was reached. If subjected to a temperature of — 15° 

 to — 20° C. the separation from the wall occurred immediately. 

 In Tradcscaiitia Jlri^iiiica, according to Ki^ihne,'^ the changes 

 before freezing are more marked but take place only when the 

 fall in temperature is abrupt and severe. The separations do not 

 always occur, especially when the cooling is slow, and seem rather 

 to be accidental contractions due to the cold stimulus, than general 

 phenomena. 



Greeleyf has shown that the reduction of temperature to near 

 zero decrees C. for a few hours will cause the animal Stciitor to 

 contract and become cyst-like, probably with the expulsion of 

 water. Threads of Spirogyra became much plasmolized under 

 similar treatment, and Livingston^ has shown that when mounted 

 in oil this plasmolysis is accompanied by an extrusion of droplets 

 of water into the oil. The effect upon both organisms is the same 

 as though they had been placed in a strong osmotic solution. 



* Kiihne, W. Untersuchungen iiber das Protoplasma. Leipzig, 1864. 



t Greeley, A. W. On the Analogy between the Effects of Loss of Water 

 ;ind the Lowering of Temperature. Amer. Journ. Physiol. 6: 1 12-128. 

 1901. 



t Livingston, B. E. The Role of Diffusion and Osmotic Pressure in 

 Plants. Chicago, 1903 (p. 75). 



