ISO 



BOTANY OF THE LIVING PLANT 



of the growing trunk affords in addition to mechanical strength, room 

 also for storage, and a means of transmission of materials. 



In the stems of Palms, where a large terminal tuft of leaves has to 

 be supported at a great height against winds, the mechanically effec- 

 tive tissues are massed towards the periphery, while the central regions 

 are softer. This may be compared with the hollow metal column 

 filled with concrete, which has the effect of preventing the metal skin 



I-'IG. 107. 



Stem of Batiiboc 11 tlu In ^ hl 1 jdc at itb upper (.■iid. Ill A it i^ seen from outside, 

 with transverse scar of the leaf-mseition, antl the eireular scar of its axillary branch. 

 In B it is cnt so as to show the hollow, and the septum which gives added strength. 

 (Reduced to 1.) 



from " buckling." On a smaller scale this construction is found also 

 in the stems of pithed Rushes and Sedges, and in many herbaceous 

 Dicotyledons. It is only a step from such arrangements to that seen 

 in the Bamboo, or on a smaller scale in the haulm of Grasses ; and in 

 some Dicotyledons, such as the Llmbelliferae. Here the thin-walled 

 pith present in the young state breaks away, leaving a central cavity 

 surrounded by a cylinder of firmer tissue. In this case the comparison 

 is with the hollow column so largely used in metal construction by 

 man. But it is liable to " buckle," as has been found in the masts and 



