360 Morpho genetic Factors 



supply. Similarly, as roots increase in size, the number of radial arms 

 increases, with the result that the xylem-phloem surface remains relatively 

 constant. 



There are many examples of this correlation between absolute size 

 and complexity of conformation, a fact which Bower (1930) was the 



N 



* 







/ 



rv* 



Fig. 16-8. The effect of absolute size on structural complexity. Steles of Lycopodium 

 scariosum of seven progressively larger sizes showing the increase in complexity that 

 accompanies increased size. ( From Bower. ) 



first to bring forcefully to the attention of botanists ( Fig. 16-8 ) . Although 

 the advantage of such a correlation is obvious, the problem of how it is 

 brought about morphogenetically is not clear. The advantage is not 

 effective physiologically until the structures are mature and functioning 

 but the pattern is laid down in the meristem. It may be that this is simply 

 a case of inheritance of a particularly advantageous developmental pat- 



