76 



PRArTTCAL rOT'RSE IN BOTANY 



examples of plant parasites, though the latter is only partially 

 parasitic, as it merely takes up the sap from the host and 



manufactures its own food 



U 



A B 



Fig. 88. — Beech root: A, grown in 

 unsterilized wood humus : p, strands of 

 fungal hypha;, associated at a, with 

 humus ; B, grown in wood humus freed 

 from fungus by sterihzation — it is not 

 provided with fungal hyphse, and has 

 root hairs, li. (A and B both several 

 times magnified.) 



by means of its green leaves. 

 86. Saprophytes. — Akin 

 to parasites are saprophytes, 

 which live on dead and decay- 

 ing vegetable matter. They 

 are only partially parasitic 

 and do not bear the haustoria 

 of true parasites. Many of 

 them, of which the Indian 

 pipe (Monotropa) and coral 

 root are familiar examples, 

 obtain their nourishment in 

 part, at least, by association with certain saprophytic fungi, 

 which enmesh their roots in a growth of threadlike fibers 

 that take the place of root hairs and absorb organic food 

 from the rich humus in 

 w^hich these plants grow. 

 Such growths are called 

 mycorrJiiza, meaning 

 " fungal roots." Similar 

 associations are formed 

 by some of the higher 

 plants also. The root- 

 lets of the common beech 

 and of certain of the 

 pine family, for instance, 

 are often enveloped in 

 a network of fungus fi- 

 bers, and in this case root Fi<- 89. —An air plant (Tillandsia), growing 

 1 • 111 on the underside of a bough. 



hairs are developed very 



poorly, or not at all. Besides greatly increasing the absorbent 

 surface by their ramification through the soil, the mycorrhizal 

 threads may possibly benefit the plant in other ways also, as. 



