i5o 



PLANT LIFE. 



In stems of trees rigidity is secured not by the distribution 

 of the mechanical tissues, but by their massiveness. In them 

 the chief mechanical tissues belong to the wood, which forms 



Fig. 170. — Diagrams showing the arrangement of mechanical tissues and vascular 

 bundles in the cross-section of various stems. The mechanical tissue is gray; the 

 vascular bundles black, with white dots. A , linden (young) ; B, a mint ; C, a sedge ; 

 D, a bamboo ; E, a grass. — After Kerner. 



a solid column occupying the center of the body. Those 

 plants which are supported by the medium in which they 

 live, such as the aquatic plants, are usually without mechan- 

 ical tissues. 



