1.^ 



Lecture 5, July 16, 1900. 



Leaves. 

 Functions of leavea. 

 1. Wliat is a leaf ? Something iDorne on a stem. Meaning of form, 

 size, arrangement, and direction of leaves. 



1. Admission of light is one function. Lead so placed that thg 

 admission of light is easy. (Photosynthesis) Hence direction is 

 involved in this particular. Perpendicular to the incident rays 

 gives most light. Shape of leaf also involved. 



Best condition for obtaining light would be for each chlorophyll 

 cell in favorable relation to the light yays, 



2. Admission of C Ot.. Same truths hold good with regard to 

 admission to CO,, but CO^is admitted on all sides. 



3. Admission of 0. Probably connected with that of CO-j^. This 

 is a universlja^ factor, common to all plants. 



4. Emission of 0. 



5. Emission of CO/^,. 



6. Emission of H^O. (Transpiration.) 



Very important. Favorable light conditions would be favorable 

 also for transpiration. Large blades favor it. Transpiration 

 in most plants comes from under side as a means of protection. 

 Transpiration "not a universal process except in aerial parts of 

 plants and probably in subtercanean parfe if soil is dry. 



7. Siiiission of liquid water from so-called water structure. 



