Biology of Higher Plants — Anatomy and Physiology 247 



ing and reducing enzymes. (2) An aid in photosynthesis by absorbing 

 usable Hght. It is known that certain anthocyanins can absorb certain 

 Hght rays which the chlorophyll cannot, thus supplying the latter with 

 energy. (3) Absorbers of heat rays which protect chlorophyll against 

 too strong light and secure a maximum of energy. Red pigments in 

 autumnal leaves and fruits absorb more energy, which hastens the matur- 

 ing and ripening processes. (4) Attractions and repellents for animals. 

 Certain colors and odors attract animals to plant flowers, thus ensuring 

 their pollination. Most insect-pollinated flowers are brightly colored 

 and have strong odors. (5) Osmotic constituents of cells. Anthocyanins 

 and other soluble pigments are important osmotic constituents of cells 

 and thus are associated with the passing of materials through cell walls. 

 Plant pigments play a very important role in the autumnal coloration 

 of leaves. This phenomenon varies from year to year in its duration and 

 in the degree of its magnificence. As cooler weather comes, the green 

 chlorophyll disintegrates. This permits the yellow carotinoid pigments 

 to become visible, and, if sugars are present, the reds and lavenders of 

 the anthocyanins also appear as they are formed. Bright days in early 

 fall produce abundant sugars upon which the bright yellows and reds 

 depend. Plants rich in sugars, such as maples and birches, are likely 

 to be bright red and yellow. Brown colors are due to flavones, and more 

 often to tannins in the cell walls. The leaves of oaks and beeches are 

 rich in tannin, hence are likely to be brown. Although the phenomenon 

 of autumnal coloration is not completely understood, sufficient data have 

 been secured to explain the process in a general way. 



QUESTIONS AND TOPICS 



1. Describe briefly each of the five general regions of the root. 



2. Discuss briefly each of the primary and secondary tissues of the mature region. 



3. Describe the general anatomy and physiology of (1) stems, (2) leaves, and 

 ( 3 ) flowers. 



4. Explain how absorption occurs and the importance of this phenomenon. 



5. Discuss the purposes of transpiration in higher plants. 



6. How are liquids conducted in higher plants? 



7. Discuss the manufacture, distribution, and storage of foods in plants. 



8. Describe the method of respiration in plants. 



9. Explain the phenomenon of correlation in plants, including the characteristics 

 and functions of auxins and heteroauxins. 



10. Discuss briefly the methods of growth in higher plants. 



11. Classify plant tropisms and give explanations for these vital phenomena. 



12. Classify plant pigments and give characteristics and functions of each pig- 

 ment. 



