132 Field, Forest, and Wayside Flowers 



dry and apparently half dead. Inside this is a 

 layer of green bark, full of sap and vitality. 



Beneath this lies the wood a hollow cylinder, 

 enclosing a light porous substance the pith. 

 This marked division of the stem into concentric 

 rings of bark, wood, and pith is found only in the 

 dicotyledons. 



In a very young plant of the rose's kin this dis- 

 tinction is not yet apparent. 



Indeed, a cross-section of any very young flower- 

 ing-plant shows a stem-tissue alike in every part. 

 In the lily's kin it all behaves alike, for any clus- 

 ter of cells anywhere in the young stalk may turn 

 into procambium. 



But when a young plant of the rose's kin is 

 about to acquire fibro - vascular bundles the little 

 clusters of cells which become instinct with con- 

 structive life lie just beneath the surface of the 

 stem. 



Next spring's bundles will develop ' in the 

 spaces between those of last spring, and by time 

 the stem is four or five years old it has a ring of 

 bast running all around it and a ring of wood 

 within. Between these, in spring, there is a circle 

 of cells which are actively at work building up new 

 tissue. 



