72 Plant Physiology 



solution plants develop a somewhat higher turgor than 

 when grown in an extremely weak solution. 



According to the work of De Vries many plant cells are 

 just plasmolyzed at a concentration of about 1.2 to 1.4 

 per cent KNO 3 (.12 to .14 gram-molecular solution), 

 which is equivalent to about 5 atmospheres. Active cells 

 of the cambium may require a concentration of from 

 .4 to .5 gram-molecular solution ; and in an investigation 

 of medullary ray cells in a common willow (Salix fragilis) 

 Kny finds that the different types of these cells are plas- 

 molyzed at concentrations varying from .10 to .8 M. 

 Moreover, turgor varies with "age, nutrition, and with 

 environmental factors, such as heat and light. 



In general, observations upon living cells render it 

 perfectly obvious that turgor is usually an essential attri- 

 bute of active cells. There is, unquestionably, an impor- 

 tant interrelation between turgor and growth; therefore, 

 conditions affecting turgescence affect simultaneously 

 all growth processes. 



45. Substances active in producing turgor. No one 

 compound or group of compounds is responsible for turgor. 

 It may be due to dissolved substances both organic and 

 inorganic, and while, in some cases, it does not change 

 materially during the growth or other activities of the 

 cell, yet the composition of the sap may undergo a rela- 

 tively great change. According to Pfeffer, the turgescence 

 of cells in the root of the sugar-beet is produced largely 

 by cane-sugar, while in the sunflower more than 40 per 

 cent may be represented by potassium nitrate. The beet 

 contains relatively little sugar when young, and the sun- 

 flower little nitrate. Various other inorganic salts, glu 



