CHAPTER IV. 



BRANCHING. 



Causes of irregular branching Wiesner's observations Branch- 

 casting Part played by animals and fungi Influence of light 

 and shade Correlation Polarity Action of gravitation 

 Internal causes of organization Action of wind in temperate 

 and Arctic countries Mechanical action of wind. 



I HAVE now to examine further causes of the irregularity 

 of branching which prevails in actual trees. 



These causes may be grouped under two distinct 

 heads. 



First, there are the specific alterations in the arrange- 

 ment and numbers of buds and the kinds of shoots they 

 produce, which are due to internal and inherited dis- 

 positions and actions in the plant : some of these actions 

 consist in the definite riddance of shoots already formed. 



Secondly, there are all the varied actions of the environ- 

 ment, due to drought, wind, rain and hail, snow and 

 ice, &c., and the attacks of other living beings which kill 

 buds, break branches, &c. and obviously destroy the sym- 

 metry by mechanical and other means. 



Both these sets of agencies may co-operate in limiting 

 the growth of particular shoots, or in stimulating that of 

 others, or in altering the directions of growth of young 



