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 (Ceratophyllum) 
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 
