REV. J. M. CEOMBIE ON THE ALGO-LICHEtf HYPOTHESIS. 279 



overcoming the difficulty. The real state of the case here may— 

 as pointed out by Nylander in a paper " On the G-onimic Evolu- 

 tion of the Colleraacei " (in 'Flora,' 1868)—" be best demonstrated 

 by attending to normal physiological conditions rather than by 

 observations founded on textures disrupted and torn asunder 

 anatomically." Now in the isidia, with which the upper surface 

 of the thallus of many species is more or less sprinkled, and 

 which are evidently propagula and entirely comparable with the 

 bulbils of Phanerogams, " we have the whole history of the evolu- 

 tion of the thallus from its first origin from a cellule containing 

 a single gonimium to a minute true Nostoc, and ultimately to 

 the perfect Collemaceous texture." Similarly, on this point he 

 states more explicitly in the ' Flora,' 1874, p. 5, that " the cellule 

 at first is observed to be empty, and then, by the aid of secretion, 

 there gradually is produced the green matter, and it assumes its 

 definite form." It follows, therefore, that Nostoc, instead of being 

 an independent algal, which according to Schwendeuerism grows 

 normally at one time as such, and becomes at another time the 

 host of a parasitic fungus, is in reality to be viewed as consti- 

 tuting the initial or rudimentary state of Collema or Lrptogium*. 

 This notion had at different times been held by many crypto- 

 gamists, though the actual transition, which is best seen in the 

 isidia, had not been witnessed by them. 



In connection with this point it has been alleged by Schwen- 

 denerians that the " cephalodia " which occur in many species of 

 Lichens, e. g. in Stereocaulei, owe their origin to certain so-called 

 " algals" — Nostoc, Stigonema, Sirosiphon, and Scytonema— insinu- 

 ating themselves into the lichen-thallus and so producing these 

 morbid excrescences. Apart, however, from other considerations, 

 it has just been pointed out by Nylander, in « Flora,' 1884, p. 220 

 (note), that the syngonimia of cephalodia (as indeed also the 

 thalline syngonimia) give no reaction with hydrochloric (muriatic) 

 acid, whereas in Nostoc, Scytonema, and Sirosiphon an ajruginose 

 reaction is always thus produced. 



It is further to be observed that in the Collemacei, where there 

 is scarcely any distinct hypotballus, this being represented only 

 in some species by a few rhizinae, the gonimia arise (as » also 



* Nylander, in 'Flora* (1868), has also pointed out that certain Glaocapt* 

 similarly constitute the thallus of various other Collemacei, e. g. Synalmaptctna, 

 S. meladermia, Collema emleseent, and Bryophagu* glaocapta, which have been 

 adduced by Schwendener as lending support to Ins theory. 



