PHYSIOLOGICAL PROCESSES IN PLANTS 95 

 Special Reports 



1. Some methods of keeping forests. 



2. Some methods of cutting timber. 



3. Circulation through stems. 



References 



Hunter, Essentials of Biology. Chap. VIII. 



Problem XVIII 



A study of leaves in relation to their environment. 

 a. Reactions of Stems and Leaves to Light 



Observations. 1. Place some plants near a light window. 

 Observe them for a few days. 



2. Place a potted plant in a dark place for a number of days. 

 Observe as above. 



Conclusions. 1. What conclusions can you make with refer- 

 ence to the effect of light on leaves and sterns ? 



2. Why are leaves spread out 

 so as to fill in all intervening 

 spaces (mosaics) ? 



b. Structure 

 1. STOMATA 



Observations. 1. Strip off a 

 bit of the under surface of a leaf 

 such as the onion, geranium, 

 lily, or tradescantia, and ex- 

 amine with the low power of a FlG 6 ._ stomataof epidermis >< 

 portable microscope. Find num- lower surface of a leaf, e, epi- 

 bers of small oval structures dermal cell ; .</, guard cell of sto- 

 (stomata). matic opening. (Tschirch.) 



2. Find two oval or kidney-shaped cells (guard cells). 

 These control the size of the opening into the leaf. 



