The Orderly Cycles Pursued in Growth 369 



most of them (the autumn foliage), a chemical accident, though 

 one with the happiest consequences to the pleasure of man. Then 

 the winter comes again and the seasonal cycle is closed. 



There remains yet one other aspect of growth, and that of no 

 little importance, — namely, the remarkable results that ensue 

 from its disturbance. All growth when left undisturbed tends of 

 itself to produce sjTnmetrical structures. In evidence thereof 

 one has only to recall the superb syimnetrj^ of an Elm or a Maple 

 when growing alone in a meadow, or the perfection of conical 

 form in a Fir tree which springs up in some field that is abandoned, 

 or the regularity in arrangement of leaves which develop within 

 the protection of a bud. And the same thing can be shown very 

 beautifully by experiment. Accordingly when a plant deviates 

 from synmietry it is always because of disturbing influences, 

 of which there are some four classes. 



Disturbance of Growth by Accidents. — These are many and so 

 obvious as hardly to need comment, including overcrowding b}^ 

 other plants, breaking of branches by wind or ice, destruction of 

 parts by animals or Fungi, scalding of newly exposed bark by the 

 sun, drying back of parts through failure in water supply, poison- 

 ing by bad gases, and many others of various sorts. And it is 

 important to observe that the destruction of parts of a plant by 

 any of these agencies is followed as a rule by an effort at replace- 

 ment and the restoration of the sjrmmetry, as can be seen in trees 

 which have lost some of their branches. 



Disturbance of Growth by Adaptive Adjustment to the Surround- 

 ings. — This subject received full treatment in an earlier chapter, 

 where it was shown that individual plants can alter greatly the 

 details of their form, size, or structure, in adjusting themselves to 

 take advantage of the best conditions of their immediate en- 

 vironments. It is most conspicuous in connection with adjust- 

 ment to hght, towards which a plant will often bend its entire 

 structure; or in connection with adjustment to moisture, towards 

 which an entire root system will often extend in a very unsym- 



