NATURE OF PLANTS 



93 



drought, transplanting, and other factors that hiiiit the annual 

 growth. They also show that the development of the plant is 

 subject to the same rhythm of growth as is seen in"the animal. 







Fig. 58. Diagram of a three-year-old stem of basswoocl cut so as to show 

 the structure in cross-section, C, in radial section, R, and in tangential stHTiion, 

 T; c, c ortcjc : cy^^^jork; ph, phloem with darker bands of stcreomc; ntc, medullary 

 ray in cross-section; mr, ray m radial section; vit, ray in tangential stxnion; 

 /, lenticels; cam, cambium cylinder; />. i^U]i»--Il. O. Hanson. 



Namely];the thickness of the rings increases yearl>- uj) to a certain 

 age, after which time there is a gradual ri'tardation. So the 

 tree has its youth, maturity and old age. 



