498 



ECOLOGY 



horizontal nutritive roots. The root systems of trees differ widely, 

 the ash, for example, having roots of great length, while the more 

 numerous roots of the beech are much shorter and finer. 



Roots as anchorage organs. In a mature plant with a complex root 

 system, a division of labor is manifest. Absorption is limited to the 

 younger portions of the roots, where there is a delicate epidermis per- 



FIGS. 708, 709. Roots of the 

 peppergrass (Lepidium) : 708, an or- 

 dinary primary root with laterals; 

 709, a root originally similar to 708, 

 but from which vigorous lateral roots 

 have developed, following the re- 

 moval of the primary root. 



meable to water and salts. Anchorage, on the other hand, is preeminently 

 the role of the much-branched root system. On the whole there is a sort 

 of correlation between the developing stems and roots, large aerial stem 

 systems commonly being associated with extensive root systems. Only 

 in certain situations, such as swamps (see p. 509), "or when there are 

 unusual winds, as during tornadoes and hurricanes, are tree " wind- 



