166 



COLLEGE BOTANY 



the -wilting of the plank However, wiltiiig may be due to 

 other causes, such as the loss of water by transpiration through 

 the foliage.. 



Osmosis ana Nutrient Salts.— The movement of water into 

 and through the plant also involves the movement of the various 

 salts which are dissolved in the water. The plasmatic membrane 



of the plant cell is permeable not ordy 

 to the nutrient saltsi but also to many 

 other substances, some of which may 

 be neutral and others injurious. How- 

 ever, it is impenetrable toi many sub- 

 stances and is therefore somewhat se- 

 lective in its functions. Some ma- 

 FiG. 97.— Three of the ceUs terials tend to accumulate in the cells 



on the left are normal and one • 'iii i i -1,1 -1 



piasmoiyzed; the cell of Spirogyra lu Considerable abundauce, although 



on the right is plasmolyzed. 



they may be of no value to the plant. 

 Methylene blue in water at the rate of 1 part in 100,000 is not 

 visible, but certain plants growing in the water will collect this 

 material in appreciable amounts. Iodine is present in sea water 

 at a dilution of about .000001 per cent., but certain sea alg-s 

 will accumulate! it in such quantities that it can be recovered 

 on a commercial basis. 



Sap and Root Pressure. — Water moves into the root system 

 and up through the stem of the plant vdth considerable force. 

 This becomes very evident when plants are pruned early in 

 the spring and is referred to as bleeding. This phenomenon is 

 known as sap and root pressure. It is very evident that the 

 various falctors concerned with the absorption and movement 

 of water in the plant, especially osmosis and turgor are im- 

 portant factors in sap and root pressure. 



