27 

 This was old physiological viow. Now it is thought that each' ' 

 substance is carried into the plant independently. Still Stahl's 

 idea is true so far as plants are ahle to use up the salts carried 

 "by the water. 



Meaning siL leaf teeth. 

 Veins go up into the point of the tooth. Hydrothode. A raised 

 s\irface gives greater opportunity for evaporation. Hence the 

 importance of the pyramid- shaped tooth of the leaf. The tooth 

 is a safety-valve to permit passage of water .;„••., 



7. Gutation . 



The hydrothode or water pore is the usual form in rxiost plants. 

 Xerophytic or sun forms have no hyfrothodes usually, hut they are 

 common in shade plants. ' Root pressure goes on, "but transpiration 

 often ceases at night. Transpiration is giving off gaseous water 

 through air spaces. Gutation is giving off liquid water through 

 veins. Hence gutation seems most important factor in deciding 

 margin of leaf. 



8. Supply of food material. 



Very important factor. WS-chter published paper on leaves of water 

 plants. He found that arrowhead leaved varied considerably in 

 going from margin out into the lake, from fxill normal leaf to a 

 petiole. It might be explained by difference in light or difference 

 in currait, but WSohter found it dependent entirely upon richness 

 or povertjr of the food supply. 



Alao cases where largest leaves are lowest. It may be because 



