2i6 LEAVES 



leaves are found in the tropics. Banana leaves are often 

 eight feet long, while palm leaves are just as large though 

 of different shape. The more severe the climate, the 

 smaller, in general, leaves tend to be. Thus it appears 

 that small leaves, in general, are an advantage to plants 

 which have to contend principally with the elements, while' 

 large leaves, in general, are an advantage to plants which 

 have to contend principally with one another. In other 

 words, small leaves go with severe climates and larger 

 ones with mild cUmates. Can you think of any possible 

 reasons for this? 



In our own cHmate large leaves are more frequent in 

 shady places than in sunny places. You find them in 

 damp woods where there is Uttle danger from drought, but 

 a good deal of danger from lack of light. Large, thin leaves 

 can make food in dim light better than small, thick 

 ones ; they take advantage of all the light there is. (See 

 Figure fS.) Direct sunKght is not essential for photo- 

 synthesis; much of it is done in diffused light such as 

 there is in shady forests. On cloudy days when the sun 

 does not shine at all, photosynthesis is reduced, but it is 

 not stopped. 



You may recall some plants with large leaves which you 

 have seen growing in the open. Do not think of these as 

 exceptions to a rule we have laid down, for we have laid 

 down no rule. Dim Hght is not the only thing which may 

 make it an advantage to have large leaves. 



In studying plant structures it is desirable to consider 

 how this form or another form of the same organ may be 

 related to the fulfillment of the laws of plant hfe ; it is 

 desirable to consider what the advantages or disadvantages 

 of this form may be as compared with another form; it 



