286 



from the fertilised egg, and that the material may be the same in both cases, or in 

 some cases by a larval stimulus. The protection to the insect in the gall is effected 

 partly mechanically, partly chemically — especially by a copious formation of tannin— 

 but the protection is not absolute. He emphasises two points — 



(a) In general no tissue elements appear in the anatomical structure of the gall 

 which do not exist elsewhere in the plant under other conditions. 



{h) All the more highly differentiated galls are produced out of juvenile tissues 

 caused to develop in an abnormal way by gall insect. The more complex 

 the gall is, the earlier must the influence producing it be exerted on the plant 



tissues. 



(2) Fungus invasion. See Annals of Botany, vol. xxiv, p. 537, July, 1910, by 

 T. Reed. The writer points out that Bernard discovered, by inoculating the cortex 

 of the roots of young plants of Solanum tuberosum with the spores of the fungus Fusarium, 

 he produced a greater yield of tubers than if not artificially inoculated. This means 

 that although the stem is removed from the roots, the former becomes infected, 

 Bernard tentatively suggests that the fungus may thus operate by giving rise to soluble 

 products which in some mysterious way cause the underground stems to swell up and 

 accumulate vast reserves of carbohydrates, &c. 



" The roots of Podocarpus are covered with small tubercles formed by a Mycorrhiza, 

 which probably assists in the nutrition of the plants, especially when young, (" The 

 Flora of South Africa " (Marloth), i, 103, with fig.) 



(3) Xerophytic conditions. See Warmings" Aecology of Plants," p. 124. 

 Bulbous and tuberous plants are mainly confined to Liliaceae, Iridacese, Amaryl- 

 lidaceae, and other families growing in dry countries, particularly in South Africa. 

 Many tubers consist of root and stem combined, as in the case of some shrubs in the 

 South American savannahs. 



(4) Qualitative influence of correlation. Goebel, " Organography of Plants," 

 Part I, p. 215, points out that if a certain part of a plant be affected (by wounding, 

 e.g.) other parts will be affected. Knight produced tubers from aerial roots, by removing 

 the subterranean stolons at an early period or by interfering with their connection 

 with the aerial parts. He produced tubers on the top of the aerial shoots, the points 

 furthest separate from the normal position oi formation of tubers. 



M.— Protuberances of the Stem. 



In reply to a correspondent, I intimated that the matter of reserves of liquids 

 in trees is principally in the Apple Tree (Angophora), a genus closely allied to Eucalyptus. 

 It is also found in a number of Eucalypts. It arises through the irregular shrinkage of 

 the rings of timber, and these get more or less filled with gum— or kino is a more correct 

 term — and when shrinkage proceeds further, being sometimes helped by bush fires, 



