Grafts etal. —124— Water in Plants 



of auxin to increase respiration (Commoner and Thimann, 1941), and 

 water intake may be tied up with respiratory activity (van Overbeek, 

 1944). Further evidence relative to the effect of certain solutes on water 

 balance in cells (Bennet-Clark and Bexon, 1946) is discussed later under 

 the subject of mechanisms. 



One of the errors claimed to be inherent in any measurement of osmotic 

 pressure is the response described as "stimulative" plasmolysis (cf. Chap- 

 ter VII). Under certain conditions, and in certain tissues, cells plasmolyze 

 in apparently hypotonic solutions, and even in distilled water. Osterhout 

 (1913) observed such phenomena in root tips of eel grass (Zostera marina). 

 The effect was ascribed to an unbalanced ionic environment, which in- 

 creased the permeability of the protoplasm, permitting osmotically active 

 solutes and water to escape and resulting in the shrinking of the protoplast. 

 Weber (1929&) observed a similar behavior in fruit flesh cells of Poly- 

 gonatum officinale that appeared to be perfectly normal. Plasmolysis oc- 

 cured when intact cells were mounted in a drop of tap or distilled water 

 containing a small amount of macerated tissue. That the effect was not 

 limited to these cells was shown by placing an Elodea leaf in the drop of 

 water, whereupon plasmolysis also appeared. Weber thought that an ac- 

 tive substance might have been released by the addition of water or by 

 slight mechanical pressure applied to the pulp, further suggesting that cer- 

 tain specialized cells contained the active material. No single explanation, 

 however, could adequately account for the phenomenon. 



Gross (1940) concluded that the plankton diatom Ditylum hrightwellii 

 does not behave as an osmotic system, due to an anomalous plasmolytic be- 

 havior which he observed. Rapid shrinking and rounding up of the proto- 

 plast was found to occur in hypotonic sea water, in a fresh water medium, 

 and even in distilled water. The response could be initiated by several 

 treatments and conditions: (a) pressure applied to the organisms by means 

 of a micro-needle, (&) change in the ionic environment — NaCl alone was 

 effective, (c) the pH of the medium — at pYi 8 the effect usually disappeared, 

 and (rf) light, prolonged absence of which caused plasmolysis. The process 

 was described as similar to resting spore formation in every respect. The 

 anomaly was such that less shrinking and plasmolysis occurred in molar su- 

 crose solutions than in more dilute solutions. The fact that rounding up 

 occurred upon transfer to dark conditions only after 16 to 24 hours, sug- 

 gested to Gross that the turgor mechanism involved osmotic work, and that 

 reserve substances present in the cells were exhausted after this length of 

 time. 



Relatively pure water is generally believed to be withdrawn on plas- 

 molysis of cells. Gross states, however, that from this particular organism 

 whole vacuolar sap is lost. No change in protoplasmic volume could be de- 

 tected; evidently imbibitional forces are not responsible. Gross favors a 

 mechanism similar to the "water secretion" of Bennet-Clark, et al. 

 (1936). 



Other examples of anomalous plasmolysis are known. Kuster (1929) 

 and Prat (1934) may be consulted for literature. It is at the present state 

 of our knowledge unprofitable to speculate as to the meaning of these so- 

 called anomalies. Nor are generalizations permissible. Just as each plant 

 has its peculiar physical and chemical architecture, so will it necessarily 

 have its own particular variation of function. Prat states that "the only 

 thing about which all the authors agree is the irregularity of the reaction." 



