RET. J. 3tf. CROMBIE ON THE ALGO-LICHEN HYPOTHESIS. 275 



the hypothallus, and between the two there is in reality no 

 distinct line of demarcation. The myelohyphas thus produced 

 contain lichenin from the very first, and in other respects present 

 the distinctive characters already mentioned. The hypothallus, 

 as developed, is closely agglutinated to and very thinly expanded 

 upon the substratum, becoming in some cases soon evanescent, 

 and in others undergoing various modifications *. In its earlier 

 stage it differs somewhat in figure, being at one time either 

 dendritically divergent or otherwise effigurate, and at another 

 time more continuous and only at the circumference plumoso- 

 radiating. The numerous specimens exhibited of Lecanora gibbosa 

 (silicole), Lecidea geographica (quartzicole), and Lecidea alboatra 

 (silicole) show the gradual evolution of the thallus from its 

 earliest hypothalline condition. In these the hypothallus is 

 blackish and radiating ; but in other lichens, such as the vitricole 

 specimen of Lecanora galactina, also exhibited, it is white, con- 

 sisting of byssine filaments laterally apposite and contiguous. 

 This hypothalline stratum, as will be apparent from what has 

 now been said, constitutes the foundation of the lichen-thallus by 

 which it is affixed to the substratum. 



Now evidently is the time when, according to Schwendenerism, 

 we ought to find the hyphae going out in quest of algae, which 

 they might lay hold of and imprison in their meshes, as " the 

 spider does the fly " in its web. But what is the actual state of 

 the case ? In all the young hypothalline formatious before you, 

 there is not the slightest vestige on the specimens of any algal, 

 Protococcus or other, which they can thus entrap, nor of any 

 gonidia developing either from the branches or from any other 

 part of the hypha? f. These, it will also be observed, whether 

 * Sometimes, as in foliaceous lichens, it appears in the form of rhizinae ; and 

 at other times, in crustaceous lichens, it is visible only as a thin line limiting the 

 thallus. 



t Dr. Minks (a disciple of Bayrhoffer), in his treatise ' Das Microgonidium ' 

 (1879), supposes that he had detected in the hyphas, and indeed in every portion 

 of the lichen-thallus, whether vegetative or reproductive, certain minute cor^ 

 puscles which he terms " microgonidia," and which constitute the initial state 

 of gonidia into which they are afterwards developed. As has elsewhere, how- 

 ever, been shown {vide Nyl. in Flora, 1879, p. 206), these so-called gonidia are 

 simply the " molecular granulations " which are found in the different cellules, 

 and which do not at all undergo the wonderful transformations indicated by 

 Dr. Minks. This is also proved by his subsequent alleged discovery of them 

 in a large number of species belonging to the Ascomycetes {vide ' Symbola? 

 Licheno-Mycologicse,' 1881), in which, as is well known, real gonidia never occur. 

 LINN. JOUHN. — BOTANY, VOL. XXI. * 



