STAGES IN PLANT EVOLUTION 



49 



The higher plants of to-day all consist of very large 

 numbers of cells forming tissues of different kinds, 

 each of which is specialized more or less, some very 



Fig. 19. A, Details of Part of the Tissues in a Stem of a Flowering Plant. 

 B, Diagram of the Whole Arrangement of Cross Section of a Stem : e, Outer 

 protecting skin ; g, green cells ; s, thick-walled strengthening cells ; p, general 

 ground tissue cells. v, Groups of special conducting tissues: x, vessels for 

 water carriage; px, first formed of the water vessels; c, growing cells to add 

 to the tissues; b, food-conducting cells; ss, strengthening cells. 



elaborately, for the performance of certain functions of 

 importance for the plant body as a whole. With the 

 increase in the number of cells forming the solid plant 

 body, the number of those living wholly cut off from the 



( C 122 ) 5 



