THE ECOLOGY OF PLANTS. 443 



deep rich humus the Bird's-nest Orchids and the Bird's-nest both 

 totally saprophytic plants (Art. 238). 



It will be noted that most of the wood-floor plants have long creeping 

 rhizomes which burrow in the humus, or short thick rhizomes giving 

 off numerous slender roots, or bulbs which grow deeply (being pulled 

 down by the contractile roots). The humus, permeated with the roots 

 of the more shallow-rooting trees, creeping Ivy stems and roots, and 

 fungus threads (in shaded woods the thick humus resembles mushroom 

 " spawn "), is occupied at different depths by these rhizomes and bulbs. 

 For instance, Yorkshire Fog, Bracken, and Bluebell often grow together, 

 but the rhizomes of the grass are just below the surface, those of the 

 Bracken creep at a lower level, while the Bluebell bulbs are dragged 

 down deeper still by the contractile roots (Fig. 182) ; the same arrange- 

 ment holds for various other groups of plants occupying the same soil. 

 In this particular case the Bluebell and the Yorkshire Fog grass send 

 up their aerial shoots in spring, before the Bracken has spread out its 

 large leaves. 



It is interesting to watch, at frequent intervals, the succession of 

 flowers in a wood throughout the year, especially in spring and early 

 summer, paying special attention to the orderly march of the spring 

 flowerers and to the underground life of the various plants in the 

 crowded soil. The succession of spring-flowers, before the trees and 

 underwood shrubs have expanded their leaves, is roughly as follows : 

 Snowdrop, Dog's Mercury, Wood Anemone, Wood Spurge, Toothwort, 

 Sweet Violet, Bluebell, Primrose, Wood Sorrel, Garlic, Yellow Arch- 

 angel, Goldilocks, and so on. 



Do not remain satisfied with merely observing the order of appearance 

 of these plants ; examine their underground parts and try to find out 

 why each appears at the time it does, how it is enabled to flower early, 

 how it competes with other plants occupying the same soil, and what 

 advantages it gains by its appearance before or after its competitors. 

 Light, moisture, temperature, habit of growth, and the time of appear- 

 ance of insects in the case of insect-pollinated flowers, are among the 

 many factors to be considered. For instance, plants which can endure 

 dense shade, e.g. Sanicle, can afford to come up later in the year ; Blue- 

 bell, Daffodil, and some other early flowerers have almost unfreezable 

 sap ; the Bracken can rapidly overgrow and overshadow low-growing 

 plants with its large spreading leaves ; and so on. 



On wood-edges we get many small trees, besides shrubs and herbs, 

 which thrive better there than under the shade of the tall trees. Note 

 the convex rounded outline of the foliage canopy at abrupt edges, 

 e.g. where the wood is traversed by a wide river or abuts on open 

 country ; the overhanging branches over a road or a stream ; the more 

 profuse branching of the trees at the edge of a wood or clump, as 

 compared with the less-branched stems and umbrella-like canopy of 

 the trees further in. Plants like Foxglove, Agrimony, Avens, etc., 

 grow commonly at the edges of woods. The vegetation of wood edges 

 shows much the same succession of plants as in the wood itself when 

 trees are blown or cut down and more light is thus admitted ; we get 

 first herbaceous plants (Bluebell, Red Campion, Wood Anemone, Wood 



