Sttbordinate and Herbaceous Flora 43 



aquatic type, the original multibranched inflorescence-axis, erected from the 

 water, affords a conspicuous example of this capacity for the retention of 

 older machinery of the land (Sparganium, Hottonia, Utricularia). Reduc- 

 tion of such a compound subaerial inflorescence-system follows rules similar 

 to those of land-forms ; problems of size of floral mechanism, anemophily, 

 and seed-output, may reduce or modify the constructions to simple spikes, or 

 ultimately to single flowers. These, again, may be affected by the relation 

 of the mechanism of adjustment of the floral axes or inflorescence axes to 

 the depth of the water, in the manner of petioles ; and further effects are 

 observed as such axes may retain photosynthetic mechanism in the manner 

 of petioles. Thus in plants with the rush-habit in leaf-members, a com- 

 parable rush-habit may be attained in the inflorescence axis (Butomus), and 

 such axes (culms) may be left as subaerial shoots when the leaves are sub- 

 merged (Scirpus lacustris). Types with floating leaves may similarly attain 

 adjusted surface-floating flowers (Nymphaea) ; but in an older phase these 

 were not so accurately managed and stood clear of the water (Nuphar, 

 Limnanthemum). In the limit, forms with submerged leaves may also fall 

 back on submerged flowers (Potamogeton densus, Zostera), and pollination 

 in the water may replace anemophily ; but even in submerged aquatics the 

 projection of the flower-spike above the surface is more usually arranged for 

 (Potamogeton lucens, Hottonia, Batrachian Ranunculi). The two systems of 

 foliage shoot and reproductive shoot require to be kept quite distinct, as are 

 their essential functions and problems. 1 



Such different types of plant-form, ranging from the timber-tree of 

 high forest to the lowliest free-floating aquatic, collectively constitute the 

 Angiosperm flora of the present world. Every tropical forest contains its 

 dominant evergreen forest-trees, with subsidiary associated epiphytes, 

 parasites, saprophytes, and climbers (lianas) ; each of these exhausting in 

 turn the possibilities of the new station and new mode of life they have 

 found, and growing in active competition with the main crop of trees, as the 

 full ecological equipment of such a forest-formation. All deciduous forest, 

 similarly, may retain examples of these primary and secondary constituents 

 of the optimum forest, with added tertiary formation of minor trees and 

 shrubs, as also a greater wealth of herbaceous ground-flora constituting the 

 underwood and woodland base. Open land beyond the forest zone is given 

 over to xerophytes, rock-plants, and prairie-forms ; swampy woodland and 

 water-courses supply all ranges of aquatics, rush-types, floating, and sub- 

 merged forms. Angiosperms, as the modern dominant race of plant-forms, 

 culminating far beyond the older Pteridophyta of the first land-surface, have 

 by this time invaded all the available biological stations of the world. 2 

 These stations present a mixed Angiosperm flora which is the effective 

 solution of the special biological problems of the environment, taking into 

 consideration the past history of the race, and the way it has come, as 

 originally seed-producing trees of high tropical forest. That is to say, the 

 story of plant-life can be only read one way. Given a tree-phylum and the 

 world to itself, there can be little doubt that in the course of time, its 

 descendants would be found modified to suit the biological conditions of 

 every special station, very much in the manner that plants do now. In 

 ancient times, preceding races of vegetation have pursued much the same 

 course, indicating that the general conditions have not greatly changed. 

 A few relics of the world of Pteridophyta in Pre-Palaeozoic times 



1 Cf. Arber (1920), loc. cit., p. 6. 



2 Just as in the parallel animal kingdom, Reptiles once dominated the land-surface, Mammals 

 do now, with aerial Bats, regressive marine Cetacea, fruit-eating monkeys, tree-eating elephants, 

 grass-eating deer and cattle, as well as carnivorous, insectivorous, herbivorous lines, all making up 

 the animal equipment of a continental area of woodland and prairie, river and sea. 



