DISCUSSION OF LICHEN REPRODUCTION i8i 



for instance in the capacity of various spermatia to germinate, though in 

 lichen spermogonia there has been apparently less change from the more 

 primitive condition. It is also possible that some process of nuclear fusion, 

 or more probably of conjugation, takes place in the ascogonial cells, and 

 that in the latter case the only fusion, as in some (or most) fungi, is between 

 the two nuclei in the ascus. 



If it be conceded that fully developed carpogonia with emergent tricho- 

 gynes, accompanied by spermogonia and spermatia, represent fertilization, 

 or the probability of fertilization, then the process may be assumed to take 

 place in a fairly large and widely distributed series of lichens. Copulation 

 between the spermatium and the trichogyne has been seen by Stahl^ Baur^ 

 and by F. Bachmann' in Collema. In Physcia pulverulenta Darbishire* could 

 not prove copulation in the earlier stages, but he found what he took to be 

 the remains of emptied spermatia adhering to the tips of old trichogynes. 

 Changes in the trichogyne following on presumed copulation have been 

 demonstrated by several workers in the CoUemaceae, and open communi- 

 cation as a result of fertilization between the cells of the ascogonium has 

 been described in two species. This coenocytic condition of the ascogonium 

 (or archicarp), considered by Darbishire and others as an evidence of fer- 

 tilization, has been demonstrated by Fitzpatrick' in the fungus Rhizina 

 undulata. The walls between the cells of the archicarp in that Ascomycete 

 became more or less open, so that the ascogenous hyphae growing from the 

 central cells were able easily to draw nutrition from the whole coenocyte, 

 but no process of fertilization in Rhizina preceded the breaking down of the 

 septa and no fusion of nuclei was observed until the stage of ascus formation. 



The real distinction between fertile and vegetative hyphae lies, according 

 to Harper*, in the relative size of the nuclei. F. Bachmann speaks of one 

 large nucleus in the spermatium of Collema pulposuin which would indicate 

 sexual function. There is however very little nuclear history of lichens known 

 at any stage until the beginning of ascus formation, when fusion of two nuclei 

 certainly take place as in fungi to form the definitive nucleus of the ascus. 



The whole matter may be summed up in Ftlnfstiick's' statement that: 

 " though research has proved as very probable that fertilization takes place, 

 it is an undoubted fact that no one has observed any such process." 



F. Final Stages of Apothecial Development 



The emergence of the lichen apothecium from the thallus, and the form 

 it takes, are of special interest, as, though it is essentially fungal in structure, 

 it is subject to various modifications entailed by symbiosis. 



' Stahl 1877. ^ Baur 1898. ' F. Bachmann 1912 and 1913. ^ Darbishire 1900. 



* Fitzpatrick 1918. " Harper 1900. ' Funfstuck 1902. 



