180 M. C. COOKE ON THE DUAL-LICHEN HYPOTHESIS. 



gonidia, does not " destroy its host plant, in the unequal struggle," 

 it cannot be a fungus, since, if it were a fungus, the gonidia would 

 be destroyed, as demonstrated by experience. Or, if it were proven 

 to be a fungus, then, not being parasitic, the gonidia are not foreign 

 to it, but a portion of its substance ; and again a dilemma occurs, 

 for no fungus is known persistently to enclose green granules. 

 Relative size is another strong presumption against parasitism. In 

 the Lichen we have a supposed parasite many times larger than 

 its host. It is an elephant parasitic upon a flea, and not a flea upon 

 an elephant. The parasite in the romance encloses and cherishes 

 its host, which is buried within its substance, reminding one strongly 

 of an entozoon, enclosed in the body of an animal, horse, dog, or 

 man. In such a case it is not usual to call the man or the animal 

 the parasite, and the entozoon the host, but the reverse. If it is 

 urged that this is not an analogy, because the entozoon is known to 

 subsist upon the animal in which it is found, then, in like manner 

 I would urge that it is not proved that the gonidia do not subsist 

 at the expense of the so-called fungus. In other words, it is more 

 feasible to suppose that the assumed green algae are parasitic than 

 that they should be the host. 



Again, if it can be shown that gonidia are part of the whole plant, 

 they cannot be distinct from the plant. If they are produced by the 

 healthy and normal action of the plant, then they are attributes of 

 the plant. If they are beneficial to the plant, acting as organs, per- 

 forming useful functions, then there is no more parasitism than in 

 the leaves of an oak or the tendrils of a vine. 



It is needless to recapitulate what has already been alleged that 

 the gonidia are generated by the plant itself, and hence there can be 

 no parasitism. 



Dr. Nylander writes : " The absurdity of such an hypothesis is 

 evident from the very consideration that it cannot be the case that 

 an organ (gonidia) should at the same time be a parasite on the 

 body of which it exercises vital functions ; for with equal propriety 

 it might be contended that the liver or spleen constitutes parasites 

 of the mammiferas. Parasitic existence is autonomous, living upon 

 a foreign body, of which nature prohibits it from being at the same 

 time an organ."* 



All conclusions as to the general character of Lichens, based upon 



* "Grevillea" ii, p. 146. 



