Primary Woodland and its Derivatives 33 



Gorse). Loss of negative geotropism tends to production of flexuous shoots, 

 the prostrate habit, and even to the case of the twining liana utilizing a 

 compensatory mechanism of transverse geotropism. Reduction of inter- 

 calary extension gives the dwarf-habit, in the limit the rosette-habit. Of 

 the common types of woodland, Corylus shows the deteriorated root-system: 

 Hedera, a climber with weak stem, shows a compensatory development of 

 adventitious roots : Lonicera is a feebly twining woody liana-form : Clematis, 

 more effective as a woody liana, climbs by means of irritable leaf-petioles : 

 Rosa becomes a scrambler by stem-spines : Rubus is even more flexuous, or 

 prostrate with the shoots freely rooting at the ends. The point is to see 

 that all plants with such equipment are at bottom forest-tree failures, 

 making the best of second-rate somatic equipment, which, when compensated 

 by greater efficiency in reproductive organization (insect-pollination, bird- 

 dispersal), so lessens the problem of wastage, that the type as a whole 

 becomes more highly organized, since continuing to give good results in 

 more difficult surroundings. However racially specialized, the underwood 

 tree, the shrub, the liana, and ultimately the herbaceous perennial, have all 

 been derived by secondary adaptations from a primal forest-tree type ; and 

 there seems to be no way of escaping this conclusion. 1 From another 

 standpoint all such derivative forms are regarded as deteriorated, so far as 

 they are less fitted to dominate the stations with optimum conditions, which 

 called forth their ancestors, though such stations are still available and are 

 occupied by their more successful contemporaries. 



IV. SUBORDINATE AND HERBACEOUS FLORA 



It is important to realize that any theory of evolution which records 

 survival and success, also takes cognizance of decadence and failure ; and 

 any analysis of the factors making for the former implies an equal necessity 

 for the consideration of the possibilities and effects of the latter ; as each 

 such factor may fail individually, or in association with others. In fact, 

 peculiar sympathy may be said to attach to failure, since every individual 

 organism which lives on this world is a failure, more or less, since it inevit- 

 ably dies. But failure in one respect may open up new avenues of pro- 

 gression in others, and thus the facts of the main evolution of plants under 

 optimum conditions are open to a wide range of variation and alteration as 

 the conditions of life are themselves changed. Thus, in a lofty tropical 

 rain-forest, where all the factors for vegetable growth are at an optimum, 

 trees compete with one another, and many fail where a few succeed. Beyond 

 the range of such a forest, with diminished value in the complex of external 

 conditions, the struggle becomes more intense as the conditions become the 

 more unfavourable, until the main fight concentrates against the environ- 

 ment rather than against other organism. As already indicated, the 

 essential structural factors for tree-dominance, are (i) the specialization of 

 a mechanically efficient main axis, carrying the weight of the plant- 

 system, (a) considerable internodal extension, giving height, (3) strong 

 negative geotropism in the growing apex, maintaining vertical orientation. 

 Where any, or all of these fail, the arboreal type deteriorates ; e. g., to a 

 small tree if insufficiently massive ; to a shrub, if the main stem loses its 



1 That is to say, it is not so easy to read the story the other way, and to trace the dominance of 

 the long-lived slowly-maturing tree as the result of the specialization of factors possessed in a 

 rudimentary condition by the herbaceous perennial; since the forest-tree is not the most paying 

 proposition biologically, and some reason has to be given for the initiation of the corresponding 

 structural characters seen in the smaller plant. 



C 



