20 

 these leaves receive best s^^viJly of food. If CO^ is more abiuir'.ant 

 near the ground then lower leaves wotild receive most. 



9. Nature of condiict inn, 

 Embryonic leaf largely veins, only matured leaves filled up. 

 Conductive tissues must be developed before chlor. tissues. Eight 

 and nine determine size of leaf or iipon amount of food material. 



10. Protection from exposure . 



Light, heat and drought. Only another way of expressing transpira- 

 tioi:i. 



11. Protection from mechanical injury . 



Either due to wind or water currents. Direction of a leaf, 

 plastic ordinarily, is greatly modified by wind or water. Ex. 

 common weed and pond weed, also Algae. 



Kerner suggest s this plasticity also explains compounf leaves, 

 as in banana leaf which has been torn by the wind. 



12. Protection from animals . 



Old view not so much accepted now. Did thistle develop spines as 

 protection against animals or did the spinous originally serve as 

 a protection ? 



13. Storagev — of air and water. 



Large leaves and petioles often come from having large storage 

 cells. Storage of food materials also modified leaves sometimes, 

 as those of a lily or onion bulb. 



14. Absorption of BaQ.' 



Ex. leaves of mosses and water plants ; also seen in hairs developed 



