94 BIOLOGY FOR BEGINNERS 



Fall of Leaves: 



1. Reasons. 



Remove waste mineral salts. 

 Lessen exposure to storms. 

 Reduce surface for transpiration. 



2. Cause of coloration. Function. 



3. Abscission layer. 



SUMMARY OF MINUTE STRUCTURE OF LEAVES 



1. Upper Epidermis. 



Structure: One layer, brick-shaped cells, few stomates. 



Cuticle sometimes present. 

 Function: Prevent loss of water. 



Concentrates sunlight on chlorophyll. 



2. Palisade Layer. 



Structure: Narrow, perpendicular cells. Contain chlorophyll. 

 Function: Regulate exposure of chlorophyll. 



3. Spongy Layer. 



(a) Spongy cells. 



Structure: Thin, irregular, loose, active. 



Function: Starch making and transpiration. 

 (6) Air spaces. 



Structure : Large irregular cavities. 



Function: Transpiration, air supply. 

 (c) Veins. 



Structure: Bundles of ducts and wood fibers. 



Function: Transportation and support. 



4. Lower Epidermis. 



Structure: Single layer of cells, many stomates. 



Function: Regulation of water and air supply via stomates. 



5. Stomates. 



Structure: Slit-like opening and guard cells. 



Function: Regulate transpiration, supply of carbon dioxide and of 



oxygen. 

 Distribution: Lower epidermis usually very numerous. 



6. Chlorophyll. 



Structure: Active green grains, rich in iron compounds. 

 Function: Photosynthesis or starch making. 

 Distribution: Palisade cells and spongy layer. 



COLLATERAL READING 



General study: Elementary Studies in Botany, Coulter, pp. 187-223; 

 Plant Life and its Uses, Coulter, pp. 201-218, 234-255; Experiments in 

 Plants, Osterhout, pp. 163-223; Familiar Trees, Mathews, pp. 1-19; 

 Plants and Their Children, Dana, pp. 135-185; Plant Relations, Coulter, pp. 

 6-52; Botany for Schools, Atkinson, pp. 70-89; Flowers, Fruits and Leaves, 



