THE ROOT 75 



however, do not get their mineral nutrients directly from 

 the soil, and these give rise to various forms suited to other 

 conditions of alimentation. 



83. Adventitious roots. — This name applies to any kinds 

 of roots that occur on stems, or in other unusual positions. 

 They may be considered as intermediate between the two 

 classes named in 81; for while their starting point is above 

 ground, they generally end by fixing themselves in the soil, 

 where they often function as normal roots. Familiar examples 

 are the roots that put out from the lower nodes of corn and 

 sugar cane stalks, and serve both to supply additional mois- 

 ture and to anchor the plant more firmly to the soil. Most 

 plants will develop adventitious roots if covered with earth, 

 or even if merely kept in contact with the ground. The 

 gardener takes advantage of this capacity when he propa- 

 gates by cuttings and layers. 



84. Water roots. — ■ These are generally white and thread- 

 like and more tender and succulent than ordinary soil roots, 

 because they have less work to do. Floating and immersed 

 plants, such as bladderwort and hornwort {Cerato-phyllum) 

 have no need of absorbent roots, since the greater part of 

 their surface is in contact with water and can absorb directly 

 what is needed. 



Land plants will often develop water roots and thrive 

 for a time if the liquid holds in solution a sufficient quantity 

 of air and mineral nutrients. Place a cutting of wandering 

 Jew in a glass of clear water, and in from four to six days it 

 will develop beautiful water roots in which both hairs and 

 cap are clearly visible to the naked eye. 



85. Haustoria, from a Latin word meaning to drain, 

 or exhaust, is a name given to the roots of parasitic plants, 

 or such as live by attaching themselves to some other living 

 organism, from which they draw their nourishment ready 

 made. Their roots are adapted to penetrating the sub- 

 stance of the host, as their victim is called, and absorbing 

 the sap from it. Dodder and mistletoe are the best-known 



