l()(j THE JOT KVU, OF HUTAN'V 



equallv firmly established before any Lichen-habit had been begun. 

 As in the t} r pical Ascomycetous Fungi, the stage of asexual sporangia] 

 reproduction enables one to visualize a still older phase of algal con- 

 struction, before the elaboration of heterogamous rainuli, when the 

 asexual sporangium was, in fact, but the apogamous modification of 

 the unilocular gametangium emitting llagellated zo'ids in the manner 

 of the hymenium of Aglaozonia and Zanardinia, or even of the 

 more remote horizons of Laminaria and Chorda. 



It is only in this way that a clear conception of the Lichen- 

 history can be approached, via a recognition of the mechanisms 

 of reproduction initiated in the sea, and following the progression (if 

 what has been termed the ' Benthic Phase.' With the aid of modern 

 sea-weeds (as in Phseophyceae and Floridese) it is possible to go back 

 step by step in the interpretation of the factors to which the special 

 case of the Lichen-fungus is the response, and to travel up through 

 all the horizons of marine progression to the problems of the sub- 

 aerial transmigration. Thus behind the heterotrophic somata of 

 these varied forms, one discerns the primary characters of the older 

 autotrophic soma in the details of the more conservative reproductive 

 ramuli ; just as in the massive parenchymatous soma of Fucus, the 

 reproductive ramalia maintain the older filamentous organization, or 

 the distinctive procarpial ramuli of the Floridese with their associated 

 assimilatory filaments may now be found wholly immersed and buried 

 within the felted texture of the smooth lamina of Dilsea edulis. 

 Similarly, while the differentiated sexual ramuli must have passed 

 through stages of heterogamous progression before they attained 

 their present condition of fertilization in situ, it is to the hymenium 

 of the asexual generation that one looks for the oldest type of 

 reproductive organ of the group — a simple unilocular structure of the 

 distant horizon even beyond the meiotic gametangium of Fucus. 



Having indicated the phyletic connection of the Lichen-fungi with 

 the modern saprophytic and parasitic Ascomycetes of the land, in 

 favour of the priority of the former, it remains to compare them 

 with the onlv living group of marine algse with which they present 

 certain features in common. Ever since the time of Sachs (1874) ', 

 land-botanists have persistently associated Lichen-fungi, and hence 

 Ascomycetes as a whole, with the great and supremely isolated group 

 of beautiful marine vegetation known as the Floridese. The point is, 

 ap-ain, to what extent is the agreement real and phyletic, or merely 

 an approximation in similar biological features of adaptation (homo- 

 plasy) in wholly distinct algal series of the past. Also, what is 

 more important — To what extent may such parallelism afford a 

 revelation of a common response to similar conditions of environ- 

 ment in the sea ? 



IV. The Story of the Flokide.i:. 



This is sufficiently well-known to admit of detailed comparison, 

 and the discrepancies are at once obvious. The Life-cycle of a 

 typical Floridean is expressed in three phases, rather than two. 



1 Sachs (1874) Textbook, Eng. Trans., 1882, p. 284, Carposporere. 



Strasburger (1912, Eng. Trans.) pp. 387-389, much emphasized. 



Thaxter (1896) Monograph of Laboulbeniacese, p. 254. " mere speculation." 



