The Growth of Stems 



151 



Fig. 



Bureau of Agriculture, P. 1. 



Rafting large bamboo stems to market in the Philippines. 



with bark that is thick and has large ridges are the ones that 

 hold their bark more tenaciously. But in all large trees the bark 

 contains only a part of the layers formed by the outer side of the 

 cambium ; much material has scaled off and fallen away. It 

 should be noted that as a tree gains in diameter, the annual rings 

 of wood in the stem are each year farther removed from the corre- 

 sponding annual layers of the bark. That is, the wood rings near- 

 est the pith are nearest in age to the outermost rings of the bark. 

 Diameter growth of perennial monocot stems. Most perennial 

 monocots, like the bamboo and asparagus, have horizontal under- 

 ground stems to which new and thicker stem segments with a 

 larger number of bundles are added each year. The aerial, erect 

 branches never increase in size after they are once mature ; but 

 the erect branches from old underground stems are from the 

 beginning much thicker than those from young plants. Con- 

 sequently, no little bamboo rod could ever grow into a bamboo 

 beam. No large bamboo beam was ever a slender rod. These 

 aerial branches come out of the ground nearly as thick as they 

 will be when mature. Asparagus plants are several years old 



