2OO 



BOTANY OF THE LIVING PLANT 



be called "phagocytes" are able to digest the fungus. They may be 

 recognised by having lobed nuclei, as seen in Fig. 150. On the one 

 side of the digestive tract are normal cells of the host ; on the other 

 there are cells of the infected region which continue to act symbioti- 

 cally. They retain the simple nucleus, and do not attack the fungal 



FIG. 151. 



Median longitudinal section of a young plant of Odontoglossum, one month after 

 infection by Rhizoctonia. s = stoma ; p = group of absorbing hairs ; p' = cells divided 

 tangentially, of which the outer will form hairs. Digestion as in Fig. 150 ; the apex is 

 not infected. (After Bernard.) ( x 120.) 



filaments. The phagocytes thus serve as -a barrier, limiting the 

 infected area, and checking the spread of the fungus into undesirable 

 parts, such as the conducting tracts, or the apical points. At the same 

 time the organic materials of the digested fungus are absorbed into the 

 host plant. Connection between the undigested filaments within and 

 the soil without is meanwhile maintained by tufts of superficial hairs 



f 



