REV. J. M. CEOMBIE ON THE ALGO-LICIIEN HTPOTHESIS. 273 



imagined. These propositions are (1) that the tissue in which 

 the gonidia of a lichen are imbedded is not of a fungoid nature ; 

 (2) that the gonidia themselves are not true Alga? ; and (3) that 

 lichens are not the expression of a condition of parasitism. But 

 though such considerations are quite sufficient for the subversion 

 of the Algo-lichen hypothesis, the crucial point of the origin of the 

 gonidia and their relation to the rest of the thallus still remains 

 to be expiscated. It is clearly not enough to show that Schwen- 

 denerism is impossible, for the mere rejection of one erroneous 

 theory would not bring us nearer to the actual solution of the 

 problem. Now the whole of the hypothesis proceeds on the 

 assumption that there is no genetic but only a parasitical relation 

 between the filamentose hyphae and the gonidia. The former part 

 of the assumption is quite correct, and the latter is entirely wrong. 

 Indeed, all researches in the way of proving a connexion, whether 

 genetic or parasitic, between these two elements is, as will pre- 

 sently appear, neither more nor less than going in quest of " a 

 mare's nest," — is an attempt to discover what has no actual exist- 

 ence. And yet the gonidia, equally with the hyphae, belong to 

 and are essential organs of the autonomous (not composite) plant 

 called a lichen. How, then, do the gonidia originate in, and how 

 are they related to, the thallus ? 



On this point, as I have already hinted, previous to the date 

 at which Speerschneider adopted and endeavoured to illustrate 

 the Bayrbofferian origin of the gonidia, there appeared in 1852 

 a valuable work by the celebrated Tulasne, entitled ' Memoire 

 pour scrvir a l'histoire des Lichens.' In the appended plates 

 by which he illustrates his researches on the morphology of 

 Lichens, there are several figures which show sufficiently well the 

 origin of the gonidia in the thallus at a very early stage of its 

 growth. These may be seen in tab. iii. ff. 1-3, in the case of 

 Lecanora cinerea, and in tab. xi. f. 17, in the case of Cladonia 

 coccifera ; though in the text the explanation which he gives of 

 their origin is occasionally in some respects rather confused. In 

 p. 3G, however, when treating of the young squamules of growing 

 Cladonia pyxidata, he, with sufficient accuracy, indicates the origin 

 of the gonidia as follows :— " Here and there upon the elementary 

 filaments (i. e. the hypothallus) some small sessile cellules are 

 generated, spheroid and colourless, which, after multiplying 

 themselves, give origin in their turn to larger cellules in which 

 the chlorophyll is collected together." So also in p. 22, when 



