CHAPTER XII. 



CHANGES OF SHAPE OTHERWISE CAUSED. 



238. BESIDES the more special causes of modification in 

 me 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. "VVe will 

 glance at them in this order. 



239. It is a familiar fact that luxuriant shoots have re- 

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

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

 result being that the lateral axes, where these are developed, 

 become in the one case far apart and in the other case neai 

 together. Fig. 255 represents a branch to the parts of which 

 the longer and shorter internodes so result- 

 ing give differential characters. A whole 

 tree being in many cases simultaneously 

 thus affected by states of the earth or the 

 air, all parts of it may have such varia- 

 tions impressed on them; and, indeed, such 

 variations, following more or less regu- 

 larly the changes of the seasuns, give to 

 many trees manifest traits of structure. 

 In Fig. 256, a shoot of Phyllocactm 



