39^ 



ECOLOGY 



carefully studied. What is the nature of the short spines ? 

 Where and how do they arise ? Distinguish between leaves , 

 and branches. Cut a section across the stem, and note how 

 much the ridges on it increase the green, assimilating sur- 

 face-tissues (Fig. 256, 1). Seedlings may easily be grown, 



and the history of the leaves 

 and spines determined (2 and 3) . 

 The cotyledons (2, 3, 4, c) are 

 entire, but the first foliage- 

 leaves (d) are trifoliate. As the 

 plant grows, the newer leaves 

 tend to produce smaller lateral 

 leaflets, and eventually the 

 centre leaflet only is produced, 

 and this is very narrow and 

 sharp - pointed, but flexible. 

 Buds arising in the leaf-axils 

 grow into shoots with narrow, 

 undivided, and sharply-pointed 

 leaves, and the branches also be- 

 come sharply pointed, harden, 

 and so form a branch-spine. 

 The development of trifoliate 

 leaves in the seedlings suggests 

 that the Gorse has probably 

 descended from an ancestor 

 with compound leaves, which 

 now only persist in the seedling 

 stage. We have already noticed 

 the interesting way in which 

 seeds of the Gorse are dispersed by ants (p. 226, Fig. 161). 

 The Sphagnum bog. The Sphagnum bog is dominated 

 by species of Bog-moss (Sphagnum) and other peat-forming 

 mosses such as the Hair-moss (Polytrichum) . It is de- 

 veloped on an impervious soil in situations where the air is 

 very moist, either at low or high levels ; and an essential 



Fig. 256. Gorse Seed- 

 lings. 1, transverse section 

 of stems ; 2, young seedling ; 

 3, older seedling ; 4, different 

 kinds of leaves on a seedling ; 

 c, cotyledon ; d to i, transition 

 from trifoliate leaf to needle- 

 leaf ; tu, root-tubercles. 



