APPENDIX A 



605 



haustoria (haw stor' i a), which can penetrate the living cells of the host and 

 absorb water and food. 



In a large number of plants, particularly those growing in forests, the function 

 of the root hairs has been partly or completely taken over by fungus filaments 



Fig. A.7. Sac fungi (ascomycetes) . Upper left, the tar spot of maple, Rhytisma; upper 

 right, the common morel found under hardwood trees, Morchella esculenta; below, a morel 

 that grows under pines, Helvetia esculenta. (Photos by Prof. Alexander H. Smith.) 



called mycorrhiza (ml' kor riz' a); these penetrate the tissues of the root, form 

 a mycelial mat about its surface, and absorb water and dissolved substances from 

 the soil. The relationship is evidently symbiotic, the green plant obtaining neces- 

 sary substances through the agency of the fungus and the latter benefiting by 

 having access to the foods elaborated by the green plant. Among the plants that 



