254 



OUTLINES OF PLANT LIFE. 



upon any plant which would furnish them similar external 

 conditions (fig. 210). 



364. {V) Mycorhiza. — Mutualism between the roots of the 

 seed plants and certain fungi is common. Such a combina- 

 tion of root and fungus is called a mycorhiza. The fungus 



Fig. 210. 



Fig. 



Fig. 21Z. 



Fig. 210. — A portion of a filament of an alga {Ectocar/tus) showing at a another alga 



{Enioderma IVittrockii) which has embedded itself in the cell-wall. Magnified 480 



diam.— After Wille. 

 Fig. 211.— a tuft of rootlets of white poplar forming mycorhiza. Natural size. — 



After Kemer. 

 Fig. 212. — Tip of a rootlet of beech {Fagus sylvatica) with fundus mantle, the loose 



hyphas acting as absorbing organs in place of root hairs. Magnified 100 diam. — After 



Frank. 



forms a jacket over the outside of the root (figs. 211, 212), 

 taking the place and work of the root hairs by means of 

 strands of hyphae extending from the surface of the fungus 

 jacket (fig. 212) ; or it grows inside the cortex and epider- 

 mis, forming knotted masses (fig. 213) ; or it is confined to 

 certain definite portions of the roots, forming upon them 

 swellings from the size of a hazelnut to the size of a man's 

 head. The first form is especially common upon the roots 

 of the oak, elm, walnut, apple, pear, maple, ash, and related 

 trees. It has also been found upon the roots of a large num- 

 ber of herbaceous plants. The second form" belongs chiefly 



