I 



THE ROOT. 7 



the stimulation of contnct with a Hupportiii^' Hurfaco, in tho samo manner 

 us tlie ailvcntitiouH (true) roots of the straw! )t!rry riniiicr aro called forth 

 by contact with the damp earth. Of this kind of mlvcnlitious roots many 

 illustrationH mi<,'ht also be adduced ; one more will suffice, the common 

 ivy {Hedera IMix L.) (Fit?. 12). 



Some plants produce a kind of adventitious roots by which they attach 

 themselves to other herbs or shrubs and draw tlieir nourishment from 

 them. The common dodder (Fig. lU) will serve as un illustration. Tho 



P10..I3.— DcxUlnr (Cm« «to), parasitic upon another plant. 



seeds of this plant germinate in the ground ; the stems grow until some 

 suitable support is reached, then twine about it and put forth a s:ort of 

 rootlets by means of which nourishment is drawn from the supporting 

 plant. Then direct communication Avith tho earth is cut off by the death 

 of the stem below the adventitious rootlets, and the plant thenceforth lives 

 as a true parasite. 



The general structure of the root does not differ greatly from that of 

 the stem. In both there is bark, woody tissue, and pith, though the last- 

 named is seldom very distinct in the root. In their modes of growth 

 there is, however, considerable difference. As already shown, the stem 

 branches according to a fiixed and regular plan, and, as will be seen later, 

 while still young elongates between the branches. In the root, on the 

 contrary, branches issue irregularly and elongation is limited to the grow- 

 ing extremity. In other worda, a root of a given length, once laid in the 



