LICHEN GONIDIA 25 



D. Theories as to the Origin of Gonidia 



Though the relationship between the gonidia within the thallus and free- 

 Hving algal organisms seemed to be proved beyond dispute, jthe manner in 

 which gonidia first originated had not yet been discovered. Bayrhoffer' 

 attacked this problem in a study of foliose and other lichens. According 

 to his observations, certain colourless cells or filaments, belonging to the 

 "gonimic" layer, grew in a downward direction and formed at their tips a 

 faintly yellowish-green cell ; it gradually enlarged and was at length thrown 

 off as a free globose gonidium, which represented the female cell. Other 

 filaments from the "lower fibrous layer" of the thallus at the same time grew 

 upwards and from them were given off somewhat similar gonidia which 

 functioned as male cells. His observations and deductions were fanciful, 

 but it must be remembered that the attachment between hypha and alga 

 in lichens is in many cases so close as to appear genetic, and also it often 

 happens that as the gonidium multiplies it becomes free from the hypha. 



In his Memoire sur les Lichens, Tulasne^ described the colourless 

 filaments as being fungal in appearance. The green cells he recognized as 

 organs of nutrition, and once and again in his paper he states that they 

 arose directly by a sort of budding process from the medullary or cortical 

 filaments, either laterally or at the apex. This apparently reasonable view 

 of their origin was confirmed by other writers on the subject: by Speer- 

 schneider' in his account of the anatomy of Usnea barbata, by de Bary^ 

 and by Schwendener' in their earlier writings. But even while de Bary 

 accepted the hyphal origin of the gonidia, he noted ^ that, accompanying 

 Opegrapha atra and other Graphideae, on the bark were to be found free 

 Chroolepus cells similar to the gonidia in the lichen thallus. He added that 

 gonidia of certain other lichens in no way differed from Protococcus cells ; 

 and as for the gelatinous lichens he declared that "either they were the 

 perfect fruiting form of Nostocaceae and Chroococcaceae — hitherto looked 

 on as algae — or that these same Nostocaceae and Chroococcaceae are algae 

 which take the form of Collema, Ephebe, etc., when attacked by an ascomy- 

 cetous fungus." 



All these investigators, and other lichenologists such as Nylander', still 

 regarded the free-living organisms identified by them as similar to the green 

 cells of the thallus, as only lichen gonidia escaped from the matrix and 

 vegetating in an independent condition. 



The old controversy has in recent years been unexpectedly reopened by 

 Elfving" who has sought again to prove the genetic origin of the green cells. 

 His method has been to examine a large series of lichens by making 

 sections of the growing areas, and he claims to have observed in every case 



' Bayrhoffer 1851. '^ Tulasne 1852. ^ Speerschneider 1854. " de Bary 1866, p. 242. 



' Schwendener i860, p. i^s- * deBary 1866, p. igi. '' Nylander 1870. * Elfving 1903 and 1913. 



