Endotrophic Mycorhiza of Ericacece. 
223 
Fig. I. Fungus tubercles on roots of Arbutus Unedo. (1) Roots with 
fungus-tubercles. (2) Section of lateral root-tubercle along plane yp in 1. e., 
epidermis; p.c., parenchymatous cortex; x., xylem ; i.x., infected xylem ; 
i.c., infected cortex ; bounded externally by layer of cork. (3) Section of 
infected rootlet along plane oe/3 in 1. m.r., mother root ; tit. mucus formed by 
bacteria; i. infected cells; A., hyphae of mycorhiza ; p., root hairs. (4) Root 
fungus, x ., brown hyphae, exogenous ; e., light yellow hyphee penetrating root. 
(5) Fungus forming spores. 
stems spring. Sections show great development of xylem (chiefly 
of medullary rays). This tubercle stores large quantities of reserve 
material, such as tannin, which exists in the cortex ; tiny fatty drops 
are seen in all cells while the medullary tract and rays are crowded 
