TBU FORMS OF LEAVES 



115 



Suggestions. — The pupil should determine why some leaves are 

 rigid (or seem to stand stifE on the plant), and why others droop and 

 hang. Is it ever because of the positions in which the leaves are borne, 

 or of some peculiarity of the petiole, or method of attachment ? Why do 

 poplar leaves shake in the slightest breeze ? Observe the lengths of 

 petioles in sunlight and in shade; also of leaves floating upon deep 

 water. Are floating leaves often peltate ? 



XXI. THE FORMS OF LEAVES 



127. The forms of leaves 

 (and of leaflets) interest us 

 in two directions, — in respect 

 to the relation which they 

 bear to the welfare and 

 history of the plant (or to 

 adaptation to particular pur- 

 poses of the plant), and 

 in respect to their use in 

 enabling us to recognize and 

 describe plants. The former 

 subject cannot be considered here. 

 We shall, therefore, define the forms 

 for purposes of description ; but in 

 doing this we must remember that 

 there is every grade of intermediate 

 form. Certain geometrical figures or 

 arbitrary ideals are taken as the 

 standards of comparison, and it must 



Fig. 11.3. 



Lanceolate leaves of 

 red pepper. 



