THE DIFFERENTIATION OF THE PLANT-BODY 29 



this purpose very completely. In other leaves of tough 

 leathery habit the delicate tissue of the mesophyll is fre- 

 quently protected from crushing by isolated thick- walled 

 cells of curious shape which extend from one epidermis 

 to the other. Others show bands of sclerenchyma sup- 

 plementing the veins and not infrequently enclosing them 

 and reaching the epidermis on each side. 



The supporting tissue is frequently known as the 



FIG. 32. DIAGRAM SHOWING THE CHIEF DISPOSITIONS OF THE SKELETAL 

 APPARATUS IN A STEM WITH FIVE COLLATERAL BUNDLES (IN TRANSVERSE 

 SECTION). 



(The sclerenchyma is black ; the bast of the bundles is white ; 

 the wood is dotted.) 



1, Type without accessory sclerenchyma ; 2, Equisetum ; 3, Bambusa ; 4, 

 Pennisetum; 5,Scirpus', 6, Erianthus ; 7, Fimbristylis ; 9,Typha; 10, 

 Juncus ; 14, Cladium. (After Van Tieghem.) 



stereome of the plant. It forms, as we have seen, the 

 most prominent part of the endo-skeleton. 



The cells of which the masses of sclerenchyma are 

 composed have been ascertained to possess almost as much 

 power of withstanding longitudinal strain as the finest 

 steel, and they are much more ductile than either this 

 metal or wrought iron. Their arrangement in the different 

 ways described has a very distinct relationship to the 

 character of the strain they have to resist. In such 



