L'L'U THE JOL'KNAL OF BOTANY 



that the more successful dominion of the land has heen attained by 

 algal forms of more mediocre attainment, so far as extreme repro- 

 ductive specialization is concerned ; i. e., they must have retained a 

 sporophyte of distinctly homologous (homothallie) construction, 

 capable of still holding its own as a free autotrophic individual 

 (Pteridophyta), with photosynthetic ramuli of freely dichotomizing 

 systems of ramification (Filicinea?) ; as, on the other hand, the 

 gametophytes retained the original method of zoidogamy by a 

 flagellated antherozoid. The Lichen Fungi, with associated spermato- 

 gamic phyla of Floride;e, Ascomycetous fungi, and Laboulbeniacese, 

 are thus left as Landmarks of Limitation, as expressing the 

 ultimate possibilities of reproductive progression in the sea. Of all 

 the heterotrophic survivors of the land the Lichens, again, present in 

 their indefinitely organized carpogonial ramuli suggestions of a phase 

 possibly as much beyond that of the very precise type of the 

 Laboulbeniacese, as it may be behind that of more siphonogamic 

 saprophytic Ascomycetes, as the least changed of all these minor 

 marine transmigrants. A common scheme of subaerial progression 

 from a wasting sea-front affords the best clue to all such secondary 

 and extreme plant-adaptations ; the different races succeeding in 

 proportion to their original equipment and the satisfactory solution of 

 their wastage problems. Beyond the elaboration of perennating 

 spore-origins they show little that is structurally new ; and, in virtue 

 of an improved method of food-supply, the whole of the older 

 mechanism of nutrition becomes more or less vestigial; though least 

 so in the Lichens with their early exploitation of algal hosts with 

 comparable metabolism. The more novel the secondary sources of 

 food-supply, the wider the races diverge in general appearance ; but 

 the constitution of the life-cycle remains unaffected, except in 

 extreme phases of decadence. The isolation of these divergent groups 

 is thus the expression of the possible modes of heterotrophic existence, 

 rallies than any indication of range of ' affinity.' The business of 

 the lichenologist is to determine the method of progression within the 

 lichen-series, bearing in mind the algal equipment of the sea and the 

 capacities of the primal transmigrants ; as the algologist has to 

 explain the conditions under which the initial types of algal soma, 

 with their potentialities and limitations, came to be evolved 1 . 



Such generalizations undoubtedly tend to promote a wider outlook 

 on these little known and often despised plants, and the details which 

 often appear merely tedious in the great wealth of genera and species. 

 As plant-monographers cease to be plant-biographers, the different 

 series tend to be relegated to the domain of specialists, and excite no 

 general interest. The present suggestions obviously touch but the 

 merest fringe of the story, but they may help to introduce the subject 

 in a new guise to many who have so far never stopped to think of the 

 meaning which may lie behind the accumulation of obscure facts. 

 The fiction of the consortium dies hard among modern lichenologist s, 

 as the dual nature took long to be generally accepted. But in the 

 storv of the subaerial transmigration a unifying system of biological 



1 But. Mem., 10 (1920). 'Somatic Organization of the Phseophyceae.' 



