IRREGULAR NL IRlTloX 



203 



in the Lurlcx. All these indications show that llu- materials »i 'he digested 

 Jungiis have been absorbed i)ito the hosi-plaut 



The saprophytic Orchid GastrocUa, which grows in Oak woo^ls in Japan. 

 [)rovides another example. The plant consists of colourless and r- 

 tubers, which may bear small daughter tubers as offsets. The inflorcs. 

 are borne only by tubers of large size, and they arc found to Ix: in v. : 

 infected by rhizomorphs of Artiiillaria mcllca, which preys on tljc ro' ■ 

 the Oak trees. The Rhizomorphs ramify on the surface of the infected tuber. 

 and penetrate through its corky coating by haustoria curiously similar lo 

 those of Cuscuta. Tlie infection spreads laterally in the cortex, but does 

 not penetrate deeply, being checked by the active resistance of the inner 

 layers, which not only control, but also digest and absorb the substance of 

 its hyphae. It thus appears that while the Khizomorph is dependent u|>on 

 the Oak, the Gastrodia is parasitic on the fungus, and depends ujMjn that 

 parasitism for its successful flowering. It is a case of parasitism at sccontl 

 hand. The attack of the Rhizomorph is tolerated, and kept under contn^l 

 by the resistant powers of the Gastrodia, so that the would-be ass<ulant. itself 

 a parasite, is compelled to disgorge. The success of the whole arr.ingement 

 depends upon the resistant powers of Gastrodia being greater than tlujse of 

 the Oak. 



It seems probable that in the coalition called endotrophic mycorhiza 

 the initiative came from the fungus, by penetration from the soil into 

 the tissues of the host-plant. The plant at first defended itself by tlic 

 digestive process, by which the intrusive fungus was kept within 

 bounds, and headed off from tissues of vital importance. Incidentally, 

 liowever, the plant gains materials by the digestion which are of value 

 for its own nutrition. The nourishment accjuircd by the fungus is 

 first worked up into the substance of its own well nourished hyphae. 

 These are then digested by the higher plant into which it \\i\s pene- 

 trated, and converted to the uses of the host. Such host plants may 

 be styled '' fungivGrous," in a sense parallel to those plants which have 

 adopted a carnivorous habit. But a nearer parallel is probably to be 

 found in tkat intra- cellular digestion, seen in the Amoeba : or in Ou 

 behaviour of the Leukocytes of the aninial body, which is a leading 

 feature in "Phagocytosis." 



An association such as that of Neottia with the fungus Rhizoctonia, 

 or of Calluna with its fungus, should not be regarded as an individual. 

 It is rather to be compared with a Lichen, being like it an obligatory 

 product of two distinct organisms. Such symbiotic conditions .\< tlic^c 

 occupy a middle position between two extremes. The t»ne is that 

 of mortal disease, where one organism of an association causes the 

 ultimate death of the other. The other extreme is that of immunity, 

 where though two organisms may be in relation, the one has no power 

 against the other. An mtermediate state between these extreme:. 



