Ecology of Woodland Plants near Huddersfield. 1g 
with open canopy (oak and birch), and is almost absent under 
shade-trees (beech, elm, and sycamore). The Bluebell (Scz//a), 
as already described in ‘The Naturalist,’ is more influenced by 
soil, being most abundant where there is a few inches of humus 
over loam, and almost absent on light sandy soil and clay. 
Two Grasses (Holcus mollis and Deschampsia or Atra flexuosa) 
are also abundant, Holcus mainly on the moist humus soils, 
and Azra on the lighter sandy parts. The author has already 
shown the common occurrence of Scz//a, Pleris, and Holcus as 
the chief constituents of the undergrowth of the Yorkshire 
valley wood, and that they occupy three distinct zones in the 
soil (see fig. 11 in ‘ Bluebell,’ ‘ Naturalist,’ March, 1904). These 
three plants are thus non-competitive in the soil, and also to 
some extent non-competitive in their erial parts, since Scz//a is 
almost finished before Pfer7s comes. To describe this kind of plant 
association Dr. Woodhead suggests the term ‘complementary 
association.’ Birks Wood is taken as an example of a typical 
mixed deciduous wood of the Coal Measure area of this part of 
Yorkshire. The second study isa typical mixed deciduous wood 
ot the plateau and slopes of the Millstone-Grit area. The woods 
actually investigated were those near Armitage Bridge, which 
lie on the slopes of the Netherton Plateau The two maps 
showing the dominant trees and the principal plants of the 
undergrowth respectively are somewhat disappointing. The 
difficulty of making charts of woods on steep slopes is here 
exemplified, and it is one which occurs in all steep-sided valleys. 
It seems to us that here the cartographer will be forced to 
abandon the horizontal representation of these woods on the 
Ordnance Maps, and in the case of studies of particular woods, 
must resort to some convention by which the wood will be 
represented as flat. The ecological results obtained in the 
Millstone Grit woods again show the influence of light and soil. 
The higher slopes have a shallow, sandy soil covered with thin 
peaty humus; the lower slopes have a deeper and moister soil, 
resulting from weathered shales. The Bracken favours the 
ground under open canopy and shuns the shade: on the lower 
slopes the conditions resemble a Coal Measure wood, and the 
undergrowth is somewhat similar; on the dry, sandy upper 
slopes the Bracken is less favoured and occurs in patches, while 
its rhizomes, being unable to penetrate deeply, are found inter- 
laced with and competing with those of the more abundant 
Ling and Bilberry. The Bracken thus occurs as one of the 
dominant plants of two plant associations, the distinction of 
1907 March 1. 
