IHE LICHEN LIFE-CYCLE 217 



other hand, in their sexual reproduction they retain vestigia of a 

 secondary mechanism of the marine process of fertilization, in terms 

 of the attachment of ' spermatia ' of sorts to a ' trichogyne ' of 

 sorts, in many respects following the lines of the Laboulbeniaceae ; 

 and, though in details as widely divergent from the analogous process 1 

 obtaining in the Floridese on the one hand, as from that of the 

 Laboulbeniaceae on the other, their method may be the one lying 

 behind the more vestigial relics traced in modern saprophytic Ascomv- 

 cetes. 



Putting these results together, one has ample reason for regarding 

 lichens as representing the relics of a distinct race, directly trans- 

 migrant from the sea, but presenting while still in the sea a somatic 

 organisation of high grade, fully complementary to the advanced 

 conditions of their reproductive mechanism and life-cycle ; and it is, 

 in turn, possible to outline the stages of their progression to subaerial 

 conditions. The same biological factors of reef-pool formation 

 which produced the Floridese, also lie behind the whole series of 

 Ascomycetes in the wider sense of aseus-bearing plants, however 

 polyphyletic in this respect. In pool-formations of standing water 

 these heterotrophic survivors have picked up intrusive alga?, to 

 recover vicariously photosynthetic relations with the free atmosphere. 

 In the same stagnant pools other types of the Laboulbeniacesej 

 originally saprophytic on abundant decaying animal forms, have 

 passed on to obligate parasitism on races of transmigrant arthropods, 

 to follow the insect-progression, and by the aid of the locomotor 

 mechanism of such organism to attain the more aerated levels, and 

 ultimately to be exposed on short-lived flies to the chances of free 

 and dry air. Similarly the Lichen-series, left exposed in the long 

 run by the periodic or permanent drying up of such ponds, indefinitely 

 progressive and regressive, becomes ultimately xerophytic in growth- 

 form, and capahle of enduring the most extreme desiccation, to 

 recover again in casual supplies of atmospheric precipitations, — thus 

 enduring conditions under which no higher transmigrant life has been 

 able to exist permanently, and finding abundant stations on exposed 

 bare rock beyond much chance of competition, to remain to the 

 present time practically at a standstill. Fertilization, if effected at 

 all, is dependent on casual rain-water, as the xerophytic Laboulbenias 

 can be only fertilized in chance moisture on the insect, or in the case 

 of the return of the latter to the water, either living or dead, — with 

 again the chances of all possible phases of sexual deterioration in 

 cytology 3 . 



1 The term ' spermatium ' was originally applied to Lichens, and was transferred 

 to Floridese (replacing ' antherozoid ') more particulary after Stahl (1877) had 

 shown their presumed function in attachment to the 'trichogyne' of Collema. 

 The Floridean ' spermatia' of Kuetzing (1843) were carpospores. On the other 

 hand the word ' trichogyne ' was definitely applied first to Florideas by Bornet 

 and Thuret (1867, Ann. Sci. Nat., p. 141), and was similarly transferred to 

 structures biologically vaguely comparable, though clearly of no morphological 

 identity, as in the cases of Coleochsete, Pyronema, Collema (rf. Sachs, 1874, Erg. 

 Trans., 1882, p. 284). and hence to Laboulbeniaceae (De Bary, 1884: Thaxter. 

 1896). 



2 Faull. Ann. Bot. xxvi. p. 350 (1912) for apogamy, pseudcgamy and phe- 

 nomena of conjugate nuclei. 



