29 

 on desert plants. Cup plant in v;est", with perfoliate leaves in wliich 

 water collects and is alasorbed by special glands. 



15. Absorption ^j^ Qrgani?:e(i food materials . 

 Utricularia, Droscera, Sarracenia. 



16. Irrigation. 



It is necessary for leaves to get rid of water which falls upon 

 them. Kerner s&ys there is a relation between dripping-points 

 of leaves and the water-supply to the roots. Spiral arrangement 

 of some plants also favors irrigation, hence it seems to partially 

 explain phyllotaxy. 



17. Secretion . 



Glands can scarcely be said to modify shape of leaves. 



18. Reproduction 



Does not usually modify leaves except in case of ferns. 



19 . Protection .ol Qth^r organs . 



Scale leaves protecting buds. In vihu.rnum scale leaves in winter 



become green in spring and develop chlor. 



20. Vlntation . 



Air spaces may also be developed for purposes of buoyancy. 



21. Mechanical necessity. 

 A last resort except 



22. Hf^r^clity. 



Something; due to past environment. Ex. Asparagus, Alao may explain 

 the phyllotaxy of leaves, venation as well. Those things which 



are least variable are most apt to be due to heredity. Variation 



