CHAPTER XII. 



CHANGES OF SHAPE OTHERWISE CAUSED. 



238. BESIDES the more special causes of modification in 

 the shapes of plants and of their parts, certain more general 

 causes must be briefly noticed. These may be described as 

 consequences of variations in the total quantities of the 

 matters and forces furnished to plants by their environments. 

 Some of the changes of form so produced are displayed by 

 plants as wholes, and others only by their parts. We will 

 glance at them in this order. 



239. It is a familiar fact that luxuriant shoots have 

 relatively-long internodes; and, conversely, that a shoot 

 dwarfed from lack of sap, has its nodes closely clustered : a 

 concomitant result being that the lateral axes, where these 

 are developed, become in the one case far apart and in the 

 other case near together. Fig. 255 represents a branch to 

 the parts of which the longer and 

 shorter internodes so resulting give 

 differential characters. A whole tree 

 \ \ i being in many cases simultaneously 



thus affected by states of the earth or 



\ r 7 the air, all parts of it may have such 



variations impressed on them; and, 

 indeed, such variations, following more 

 or less regularly the changes of the 

 seasons, give to many trees manifest 

 178 



