338 MR. T. W. WOODHEAD ON THE 
unsuccessful attempts to show the distribution of the various 
species on one map, it was decided to map the more abundant 
species separately. The commonest and most striking plant is 
the Bracken (Pteris aquilina), and it was therefore taken first. 
Fig. 2 shows its distribution. A comparison of the tree-map 
with this suggested unmistakably that the distribution of 
Braeken was determined to a considerable extent by the 
dominant tree: that under trees with an open canopy like Oak 
and Birch, which, while affording much protection, admit a 
large amount of light, the Bracken flourishes ; but under trees 
Fig. 1. 
oo Fagus sylvatica . 
aon s montana. 
^A Acer pseudoplatanus. 
AAA Copuzors. 
Birks Woop. 
Map showing the distribution of Trees, 
with a close canopy, such as Sycamore, Elm, and Beech, much 
light is eut off; and a comparison of figs. 1 and 2 will show that 
in these areas Bracken is almost or entirely absent—that is, the 
shade produced is evidently an important factor in limiting its 
distribution. 
Thirty years ago little or no Bracken occurred here, but at 
that time there was an extensive shrubby undergrowth, espe- 
cially of Hazel. The depredations of rabbits, however, was such 
