196 



The Living Plant 



tairied in the older jiart of the root, where the entire anatomy is 

 closely like that of the stem. Roots, however, have no nodes, 

 nor regular places of origin of new roots, which, unlike branches, 

 originate deep in the tissues, budding out as it were, from the 



fibro-vascular bundles (figure 67), 

 and breaking their way (partially 

 by the aid of enzymes) out 

 through the cortex, at places de- 

 termined by the stimulus of more 

 abundant air, water, minerals, or 

 space. This method of origin of 

 side roots, by the way, stands in 

 marked contrast with that of side 

 stems, or branches, which always 

 originate by a transformation of 

 the cells of the cortex, as indi- 



FiG. 67. — A cross section of a typical i • <2 i ot t^i i-i, 



root, showing the way in which a side Cated m HgUre 137. IhUS, the 



fn:r:S-by^g:rka^t; root system of any plant is al- 



Curtis- Nature and Development of ^^^yg eXCeSSively irregular, al- 

 Plants.) ^ ^ D 7^ 



though, on the other hand, differ- 

 ent kinds of roots present comparatively little variation in 

 structure or appearance, as indeed is to be expected from the 

 comparatively uniform conditions under which most of them live. 

 Typically, roots are much more slender than stems, and have 

 their strengthening tissues condensed nearer the center, in obvi- 

 ous correlation with the fact that they have no lateral strains 

 to withstand, but only pulling strains exerted upon them by the 

 stems for which they must provide a firm anchorage. Therefore, 

 while stems approximate to hollow columns in construction, roots 

 approximate rather to ropes or cables. Indeed, in many roots, 

 one can trace a distinction between features connected with 

 absorption and others connected with anchorage of the stems; 

 and the difference in some cases goes so far that one distinguishes 

 between absorbing roots and anchorage roots, which often occupy 



