34 Plant-life of the Oxford District 



leadership ; to a scrambling or prostrate shoot-system, where the negative 

 geotropism fails. Again, among a mass of competing trees, the primary 

 struggle is to secure some sort of substratum, implying a connexion with 

 the soil and its food-salt supply. Failures can only become attached to 

 other organisms, as (i) Parasites, (2) Epiphytes, (3) Climbers, or (4) live as 

 Saprophytes on decaying debris at the forest base. Parasites, making 

 vicarious haustorial connexion with the transpiration-current of their host, 

 may retain the woody habit. Climbers, utilizing the possibilities of inflor- 

 escence-tendrils, leaf-tendrils, root-attachment, or a special mechanism of 

 transverse geotropism giving the twining habit, may remain arboreal to a 

 limited extent. But Saprophytes, losing their photosynthetic mechanism 

 (holosaphrophytes), are never woody, and Epiphytes only acquire the 

 arboreal habit as their roots reach down to the soil. For example, the 

 source of essential phosphate for an epiphytic orchid, living possibly 200 ft. 

 high up on the branch of a tree, must be precarious to the last degree. 

 Again, in such a closed formation, one wonders what becomes of all the 

 output of seeds by the dominant trees ; but even in the best regulated forest 

 there are chances of accident, the largest trees must fail and fall at some 

 time ; tempest, lightning, and even earthquakes, may have to be reckoned 

 with. So that even if the entire forest be demolished, provision for imme- 

 diate regeneration has to be kept in reserve, as a necessary part of the 

 wastage-problem of the race. Every optimum tropical forest thus carries 

 its normally associated equipment of such forest-tree failures. 



In more open forest, with the introduction of the deciduous habit, and 

 less favourable conditions for tree-development, reduced shrubs and herba- 

 ceous forms acquire a new significance ; and the latter, having served so 

 long an apprenticeship to starvation, may now live and reproduce on the 

 food-material gained in a shorter season than can a tree. In this way, as 

 the conditions for tree-growth become more unfavourable, the herbaceous 

 perennial acquires a greater preponderance in the flora. That is to say, 

 even the optimum forest must come to an end somewhere ; in space, as the 

 conditions of soil and temperature change for the worse, and by time-factors, 

 as seasonal extremes become more and more marked. Hence, though 

 throughout all the ages, the evolutionary progression of the forest-tree is 

 the main theme of Botany, there has been always a constant stream of 

 phyletic debris of such races, which, failing in the full arboreal habit, may 

 nevertheless make a working-success of some alternative line of existence. 

 It is, in fact, the special property of the intensive energizing action of 

 plasmic matter, which we call ' Life ', to respond in the course of time to 

 every possibility of environmental complex ; and since we, as a human race, 

 have left the tropical forest-zone, the more inferior types of vegetative 

 organism, as herbaceous plants which have also lost the arboreal habit 

 (though in a different sense), appeal to us as more noteworthy in their 

 solution of the many complex problems of extra-forest land. 



Origin of Herbaceous Plants. The case of the plant which never 

 makes more than the first year's wood, introduces the type which gives the 

 greatest range of variety in all modern flora, as the one which carries the 

 principle of quick returns to the seasonal limit of seed-production on special 

 shoots of one year's growth, followed normally by exhaustion and death of 

 these axes after fruiting ; perennation being maintained by parts at the 

 soil-level, or below ground, in a definite rhizome (root-stock) region, which 

 may itself be even massive and woody, but does not commonly appear above 

 ground. Such extreme changes may appear within the limits of a con- 

 ventional genus ; since generic characters are commonly founded on the 

 reproductive (floral) mechanism, as involving more deeply seated factors of 



