6 



KLKMENTS OF HOTANY. 



tlowod mnwy i)lmitH willi flio power of jjuttin^' fortli roots ns occasion may 

 require from uuy part of the stoin, or cvon, in nonio iustanceH, from tho 

 loaves, tliUH f^'iviii^ tlicm a (loul)l(' liold on lifo : such are dcnominatod 

 secondary or adventitious roots. The common Htra\vi)crry of onr 

 gardens will servo as an illustration of on(( kind of adventitious roots. 

 This i)lant 2irodiicos "runners,"' which put forth roots at the point where 

 they touch ground, then a cluster of leaves, and a new jjlant is formed. 

 The stems of the rnuning Mackherry (/lulniti ( '(inatlensis L. ) often root freely 

 also, and form a netting for the feet of the nnwary. Very many illustra- 

 tions of plants endowed with tlun power might be found anywhere about 



Fig. ]2.--Conimon ivy (lledera Ifellsi-), with nilvoiUitioua roots. 



lis, bnt it remains for the skilful gardener to develop it to its fullest er- 

 tent, as his cuttings of roses, geraniums, and indeed of almost all his rarest 

 and most beautiful l)looming plants abundantly testify. 



Such ad'ventitious roots are, however, true roots, which perform the 

 ordinarv functions of such organs. There are other adventitious roots of 

 an entirely ditYerent character. The stem of the poison ivy (lihus Toxicoden- 

 dron L.), when growing beside some object to which it can cling, puts 

 forth roots in innumcr.iblo numbers which do not contribute in any de- 

 gree whatever to the nourishment of the plant, but merely aftbrd mechan- 

 ical sui)port. Moreover, these roots appear to be produced in response to 



