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STUDIES IN SYMBIOSIS, ii., 



tubercles or apogeotropic roots of this genus first came under my notice several 

 years ago when examining seedlings of various stages collected at Woy Woy, 

 N.S.W., in the midst of a dense formation of Macrosamia growing on a sandy 

 soil. Since then seedlings raised in pots of sandy soil in the Botanical Garden 

 of the University of Sydney, and even in glass-stoppered jars, have frequently 

 developed similar tubercles. 



Text-fig. la. — Young seedling of Macrozamia spiralis showing seed (s), 

 hypocotyl (h), first leaf (1), tap-root (t.r.), and tubercles 

 (T) just above soil level- Note that these root-tubercles 

 are negatively geotropic. (x 2/3). 



Text-fig. lb.- — Single tubercle of Macrozamia showing loose papillose 

 surface (s) of the upper part of root, (x 2/3). 



Text-fig. 2, — Older seedling of Macrozarnia showing main tap-root (tr.), 

 four tubercle roots (T), normal secondary roots (s.r). 

 bases of two leaves (1), hypocotyl (h) and seed, (x 2/3) . 



Text-fig. 3. — Seedling of Macrozamia showing tubercles (T), developed 

 as the result of inoculating the tap-root (t.r.), and the 

 secondary roots (s.r.) with a pure culture of Macrozamia- 

 bacteria. In each case the root tubercles develop close 

 to the point of inoculation, (x 2/3). 



The tubercles are not of universal occurrence on seedlings; in some eases 

 many tubercles are developed, in others none at all, while in the great majority 

 of cases, the tubercles are few in number. In Macrozamia the tubercles do not 

 form such large coral-like growths as in Cycas revoluta, but each individual 



