THE LEAF. 61 



PHYSIOLOGY OP LEAVES. 

 Protection. 



Leaves require protection against 



1. Changes of temperature. 



2. Drying. 



3. Attacks of animals, fungi, etc. 



4. Injury by wind and other meteorological agencies. 



Cf. Lubbock, Flowers, Fruits, and Leaves, Chap. 

 VI ; Kerner, Flowers and their Unbidden Guests. 



Some of the following observations are to be carried out 

 in the laboratory, while others are best conducted out of 

 doors. 



I. Remove the epidermis from a portion of a hyacinth 

 leaf, or the leaf of some other fleshy plant. Notice its 

 texture, strength, and elasticity. After a time observe 

 any changes that have taken place in the part from which 

 the epidermis has been removed. 



II. Examine the hairy covering of leaves of common 

 mullein. Compare other hairy plants. Examine micro- 

 scopically the hairs of mullein, verbena, rose geranium, and 

 other common species. Make a series of drawings illus- 

 trating the epidermal appendages of various leaves. 



III. Study the leaves of the Austrian pine, common 

 juniper, and other conifers. Enumerate the protective 

 arrangements exhibited by them. 



IV. Compare very young leaves of the oak, apple, or 

 other common tree, with older ones. 



V. Many plants are protected by disagreeable or poi- 

 sonous substances stored in their foliage. Name any of 

 these that you know. 



