Lecture VIII — 113 — Mycodomatia 



is maximum. Miege (1936) found that refrigeration for not longer 

 than 4-5 months restored vitality to the potato quite as well as a change 

 in altitude. Loss of the endophyte in this fashion explains Jumelle's 

 (1905) problem of why the isolated Fusariiim seemed to have little 

 importance in tuberisation of 5". tuberosum and 6". Commersonii. In- 

 deed, Castan (1941) concluded that a symbiotic fungus is not neces- 

 sary to tuberisation, at least at low altitudes. 



These statements were modified somewhat by Costantin (1936). 

 Thus, while tubers of cultivated potato do not contain symbiotic 

 fungi, certain varieties contain mycorrhizal fungi just as the wild 

 forms. Furthermore, while infestation is usually abundant, it may 

 be sparse or completely lacking in certain individuals. Again, 

 in late summer at high altitudes, small ("microscopic") tubers 

 were formed in conjunction with symbiotic fungi that, left in the soil, 

 spontaneously reproduce the plant ; but at lower altitudes the sym- 

 biotic fungi are lacking and the tubers perish during the winter. This 

 action was confirmed by Joseph (1935), who notes also that "micro- 

 scopic" tubers dilTer in colour. 



Melampyrum: — M. prate use utilizes the humus of the moss, or 

 grass, tussocks in which it lives through delicate protuberances or ab- 

 sorptive organs produced from the roots. These protuberances were 

 found actually growing intO' dead objects (Koch, 1887). 



Orobanche: — Henfrey (1849) suggested that the whole tuberous 

 base of the plant is concerned in absorption, just as in orchids. Further 

 studies of mycotrophy in this plant are awaited. 



Composites: — Molliard (1920) has been mentioned already for 

 his work on radish and carrot : under similar sterile conditions he was 

 able to induce tuber-formation in Dahlia, that is, under optimum con- 

 ditions of sugar and COo supply. Swollen adventive roots were formed 

 within 6 weeks, and Molliard concluded that "under favourable 

 conditions" micro-organisms are not necessary to tuber formation, — 

 although it is not explained how plants in nature are to secure flasks, 

 sugar solutions and rubber stoppers as substitutes for the aforemen- 

 tioned endophytes. An actinomycosis is described by Dufrenoy 

 (1920) for Adenostyles, but he does not state definitely that there is 

 an enlargement of the tissues. 



Juncus: — Tubers on Jimciis were mentioned by Chatin in 1856, 

 also by Cameron in 1886, who found root-swellings likewise on 

 Ruppia maritinia, R. rostella and Eriophorum vaginatiim. Weber 



