76 



FOUNDATIONS OF BIOLOGY 



individual and the production of 

 other similar individuals, reproduc- 

 tion. 



In order to obtain a mental picture 

 of the essential working plan of the 

 tissue distribution in the body of a 

 higher Flowering Plant, we shall con- 





FIG. 41 . Ideal vertical section through a generalized 

 plant, showing the typical distribution of the systems 

 of tissues. The central cylinder, or stele, comprises the 

 pith (coarse dotted), xylem (diagonally lined), phloem 

 (cross lined), with cambium (fine dotted)- between and 

 extending to growing points of root and shoot. The 

 cortical system (crosses) forms the 'hollow' cylinder 

 which surrounds the central cylinder and is, in turn, 

 enclosed by the outer hollow cylinder (double lined), 

 or dermal system. (From Ganong.) 



sider first an ideal vertical section 

 through a generalized plant. (Figs. 

 41, 43, a.) 



The root and shoot system together 

 constitute a continuous body, which 

 may be regarded as forming a long 

 narrow cylinder of cells, the bottom 

 of which is the growing point of the 

 primary root, and the top, the grow- 

 ing point of the shoot. This primary 

 cylinder, in turn, is made up of a solid 

 central cylinder of cells, surrounded 

 by two concentric 'hollow 1 cylinders. 

 The inner of these concentric hollow 

 cylinders surrounds the central cyl- 

 inder, and in turn is surrounded by 



