TUBER1ZATION SIS 



seedlings with slender stems and with leaves borne at distinct in- 

 ternodes, whereas in the presence of the endophyte the axes of the 

 seedlings are thick, the internodes short, and the leaves crowded. 

 These observations led her to conclude that a causal relationship 

 between invasion by the endophyte and tuberization exists and 

 also induced her to explore the possibility that fungi are the cause 

 of tuberization in Ranunculus ficariae and Solamim tuberosum 

 [ Bernard (1911), Bernard and Magrou (1911)1. After Bernard's 

 untimely death the experiments were continued by Magrou 

 (1921, 1924). He observed mycorrhizae in Solanum magia, pre- 

 sumably an ancestor of the cultivated potato, and 5. dulcamara 

 and named the associated fungus Mucor solani. He reported that 

 this fungus was capable of infecting Solanum tuberosum raised 

 from sterilized seed. His observations and conclusions have not 

 remained unchallenged, however, and in fairness may be said to 

 require confirmation by the performance of a series of synthetic 

 experiments. Only on the basis of such experiments can his find- 

 ings be accepted or discarded. There still remains the interesting 

 possibility that the endophyte may provide the stimulus that ini- 

 tiates tuberization, and that it may be entirely digested by the host 

 cells by the time the tuber is mature. 



Constantin (1922) summarized his studies of tuberization as 

 follows: "The association of perennial species of plants with soil 

 fungi has brought about a permanent symbiosis— a condition 

 which does not occur with annual species. Since the perennial 

 character in plants is due to the low temperatures of high altitudes 

 and latitudes, cold climates may be considered as favorable to the 

 establishment of symbiosis. Cultivated potatoes have lost the 

 mycorrhizal relations of the primitive forms to which tuberization 

 was due, and in order to produce tubers without this relationship 

 they must be grown in cold climates." 



The recent report of Lutmari (1945) directs attention to Ac- 

 tinomycetes within tubers of potato and the roots of artichoke, 

 parsnip, carrot, and beet. The filaments, demonstrable by special 

 stains, pass between the cells and are intimately applied to them. 

 Their role remains unknown, but Lutman concludes, "The effects 

 of actinomyces filaments surrounding every cell cannot, at this 

 time, be even estimated, but the materials which they withdraw 

 from the cells and the products which they excrete and which 



