Kelley — 112 — Mycotrophy 



that tuber formation is not dependent on the fungus per se but to a 

 certain sap concentration, for cuttings of potato plants placed in 

 aqueous sugar solutions produced tubers. This discovery he at- 

 tributed to Marchal. a critical concentration exists for each plant ; 

 and Bernard thought that tuberisation in all cases depends directly 

 upon a certain degree of concentration of cell sap. But ordinarily 

 the habitual provider of this sap concentration is a fungal parasite 

 {\902b), which produces the optimum concentration for diastasic 

 ferments. Bernard grew the fungus, Fusarimn solani, in a macera- 

 tion of potato sap and found it increased the sap concentration as 

 indicated by a lowering of the freezing point. 



That tuber formation is connected with sap phenomena was in- 

 dicated further by the work of Rolfs (1901), who found that small 

 tubers were formed on the stem when a stricture was placed about the 

 stem, either by the fungus or by artificial girdling, and the sap was 

 prevented from flowing to the region of tuber formation. It may be 

 noted incidentally that presence of glucose in concentrations of 1/100 

 to 1/10 mol. is termed essential to cell division and elongation in wheat 

 roots (Burstrom, 1941). But Molliard (1915) found that even 

 when the plant is placed in a sugar solution there was no tuber forma- 

 tion until gaseous interchange (which increased sugar absorption) was 

 suppressed. Magrou finds that normal tuberisation may be obtained 

 glucose (also glycerine), in combination with action of light (Ann. 

 d. Sci. Nat., Bot., XI, 5:135-136, 1944). 



Believing that tuber formation is always induced by fungi, Bernard 

 (1911) investigated other plants and found that 6". Dulcamara and 

 S. Maglia (the latter from Chile) also contained an endophyte. Janse 

 (1897) had found the same for S. verbascifolium in Java. Magrou 

 (1914) found furthermore that the endophyte of S. Dulcamara could 

 induce tuber-formation in S. tuberosum, hence there is no necessarily 

 specific endophyte ; and this observation was confirmed by Costantin 

 (1935). Yet under cultivation the endophytic fungus is lost and the 

 potato plant produces tubers without it (Magrou, 1921; Castan, 

 1941) ; and the suggestion is made that dunging destroys the fungus, — 

 which still lives in the wild form, ^S. Maglia of Chile . With further 

 study it was concluded that tuber formation in the potato is an "ac- 

 quired habit" of the plant in cold climates, the climate having the same 

 sort of action in tuber formation as the fungus ; for the potato in 

 cold climates, either in high latitudes or in high altitudes, produces 

 tubers normally whereas in warm climates this power is lost (Costan- 

 tin, 1922). Potatoes grown at 1400 m. produces more tubers than 

 those at 560 m. (Costantin, 1935a), a result confirming Lebard 

 & Magrou ( 1935), who found that there is an altitude where the yield 



