226 



PLANT SOCIETIES 



Even in the same species or kind, individual plants differ 

 in color; and this individuality usually distinguis;lies the 

 plant year by year. That is, an oak Avhich is maroon- 

 red this autumn is likely 

 to exhibit that color every 

 year. The autumn color 

 is associated with I he 

 natural maturity and 

 death of the leaf, but it is 

 most brilliant in lonj^'and 

 open falls — largely be- 

 cause the foliage ripens 

 more gradually and i)er- 

 sists longer in such sea- 

 sons. It is probable that 

 the autumn tints are of 

 no utility to the plant. 

 The yellows seem to be 



due to the breaking down 



f ^^^p^ffi and disorganization of the 



I'hlorophyll. Some of the 



intermediate shades are 



*L '>'j'mM pi'obably due to the un- 



^ T^W^ masking or liberating (jf 



normal cell color -bodies 

 which are covered with oi- 

 obscured bj^ chlorophyll in the growing season. The reds 

 are due to changes in the color of the cell sap. 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. 



369. ECOLOGY.— The study of the relationships of 

 plants and animals to each other and to seasons and envi- 

 ronments is known as ecology (still written occology in 

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



