234 



PLANT SOCIETIES 



is likely to exhibit that color every year. The autumn color 

 is associated with the natural maturity and death of the 

 leaf, but it is most brilliant in long and open falls — largely 

 because the foliage ripens more gradually and persists longer 

 in such seasons. It is probable that the autumn tints are 



of no utility to the plant. 

 The yellows seem to be 

 due in part to the break- 

 ing down and disorganiza- 

 tion of the chlorophyll. 

 Some of the intermediate 

 shades are probably due 

 to the unmasking or liber- 

 ating of normal cell color- 

 bodies which are covered 

 with chlorophyll or ob- 

 scured by it in the grow- 

 ing season. The reds are 

 due to changes in the color 

 of the cell-sap, or to the 

 unmasking of the red by 

 the disintegration of the 

 chlorophyll. Autumn 

 colors are not caused by 

 frost. Because of the long, 

 dry falls and the great 

 variety of plants, the 

 autumnal color of the 

 American landscape is phenomenal. 



397. Ecology. — The study of the relationships of plants 

 and animals to each other and to seasons and environ- 

 ments is known as ecology (still written cecology in some 

 dictionaries). All the discussions in Part II of this book 

 are really different phases of this subject. It considers 

 the habits, habitats and modes of life of living things— 



403. Three society zones- 

 forest. 



-bog, forest rim, 



