Conditions and Principles of Absorption 71 



plasmolysis is taken as the measure of the turgor of the 

 cell. 



Plasmolysis may be regarded as a general phenomenon, 

 yet it should be observed that the cytoplasm may undergo 

 contraction, wholly independent of osmotic relations, under 

 the influence of certain stimuli. Greeley l ascertained 

 that low temperature may produce this effect, and under 

 certain circumstances high temperature may also cause 

 contraction. It has long been known that injurious sub- 

 stances may produce plasmolysis coincident with injury, 

 a fact to which also Osterhout '- has recently called atten- 

 tion. 



44. Variation in turgor. - - Considering plants as a 

 whole, thus including fungi, algse, and the higher plants, 

 there is great variability in turgor. The fungi show the 

 greatest range and are therefore adapted to thrive in the 

 most diverse situations with respect to concentration. 

 Fresh-water algae and all the higher plants show, on the 

 whole, a less extensive range; yet even in the same plant 

 the cells of different parts, or tissues, may show no signifi- 

 cant variation. Commonly, as already suggested, the tur- 

 gor in many epidermal and parenchyma cells is equiva- 

 lent to about 7 per cent of sugar (4.5 atmospheres, but 

 often the range may be from 4 to 8 atmospheres). This 

 fairly close range in the higher plants is perhaps to be 

 anticipated, since it is not conceivable that the strength 

 of the soil solution, under the complex physical and chemi- 

 cal conditions, would show unusual extremes. It may be 

 readily shown by experiment, however, that in a strong 



1 Greeley, A. W., Am. Journ. Physiol., 6: 112-128, 1901. 



2 Osterhout, W. J. V., On Plasmolysis. Dot. Gaz., 46 : 53-55, 1908. 



