Lecture VIII — 111 — Mycodomatia 



copious nodules of various sizes and forms which appear as little 

 clubs although they may have a very delicate continuation as a thin 

 rootlet. In section they are seen to have a central cylinder with pro- 

 nounced water tissue and peripherally a normal cortical tissue, von 

 TuBEUF thought that neither fungi nor bacteria are responsible for 

 these structures. He found them on all woody plants of the moor 

 except pine, that is, on six ericads including Calluna and Andromeda. 



But for Arbutus, true mycodomatia caused by a fungus are de- 

 scribed by RiVETT (1924) and by Dufrenoy (1917). Inoculated 

 rootlets developed into small pear-shaped tubercles, said Dufrenoy, 

 on which nearly all the epidermal cells develop into root-hairs, around 

 which algae and bacteria collect and form a mucous. The fungus in- 

 vades external layers of cortex which stores large quantities of re- 

 serve material as "tannin" while medullary tract and rays are crowded 

 with starch grains. Rivett, in describing the endophyte in old tu- 

 bercles, said that infection by fungus keeps pace with production of 

 new cells by growing point, and digestion and reinfection proceed 

 successively. Thus peripheral cells, except at growing points, are to 

 be found filled with partially digested hyphae. Digestion proceeds 

 all the time that tubercles are growing and even in winter it is hard 

 to find clearly defined hyphae. In a great majority of the cells cavities 

 are filled with a granular mass of deeply staining material in midst 

 of which persists a large nucleus. Endodermal sheath becomes densely 

 filled with reserve, and the conducting tissue itself becomes blocked 

 with deeply staining material. Tubercles persist in this condition 

 throughout winter and early spring. 



Pyrola rotundifolia possesses tubers formed by inordinate radial 

 increase in size of epidermal cells as result of fungal infection. At 

 first the hyphae are intercellular but later they penetrate the cells and 

 fill them ; the nuclei become hypertrophied and then disappear. A 

 mantle is finally formed about the root (Kramai', 1899). 



Solanum: — Tuber formation of the potato, according to Ber- 

 nard's early work (1901) is called forth by an endophytic fungus, 

 Fusarhwi solani (later called Rhisoctonia solani). In pure culture 

 with the fungus, tubers were freely produced while in soil that was 

 little infested tubers were sparse. He said that, according to state- 

 ments made by de l'Ecluse in 1601, when potato seed was first 

 planted in Europe, flowering but not tuber-forming plants were pro- 

 duced, so that to secure a crop of tubers, older tubers rather than seed 

 had to be planted. Today, plants grown from seed produce tubers the 

 first year because with general cultivation of the potato the fungus is 

 widely distributed in the soil. Bernard noted still further (1902a) 



