11] WOODLAND ASSOCIATIONS 57 
been described in some detail by Woodhead (1906 : 336, et seq.). 
In the case of a particular wood near Huddersfield, Woodhead 
showed by means of sketch maps that under trees like the 
oak and the birch, which admit a large amount of light, the 
bracken flourishes; but under trees with a much closer 
canopy, such as the wych elm, sycamore [introduced], and 
beech [introduced], much light is cut off, and the bracken is 
almost or entirely absent. Woodhead applied the same method 
to another plant, the bluebell (Scilla non-scripta), in the same 
wood. In this case, he found that light is not the [only] 
controlling factor, but that the plant is most abundant in a 
lighter, loamy soil where more shade occurred. The bluebell 
also occurs in stiffer soils simulating clay, and here competes 
with the yellow dead-nettle (Lamiwm Galeobdolon), the dog’s 
mercury (Mercurialis perennis), the cuckoo-pint (Arum macu- 
latum), and numerous root-branches of small trees. In shallow, 
sandy soil mixed with humus, the bluebell only occurs in 
straggling patches. On such soils, the bluebell does not 
form those unbroken stretches so characteristic of moist areas 
(cf. figure 5). The grassy vegetation of many of these woods 
is mainly composed of Holcus mollis and Deschampsia flexuosa. 
The latter species prefers an acidic,-humous soil, where it is 
associated with Galiwm saxatile, Vaccinium Myrtillus, Teucriwm 
Scorodonia, and Solidago Virgaurea. 
The plant society in which the bracken (Pterzs aquilina) is 
associated with Holcus mollis, Woodhead (loc. cit.) termed a 
“ meso-Pteridetum,” and that in which the bracken is associated 
with Deschampsia flexuosa he termed a “ xero-Pteridetum.” 
These terms, however, are not very satisfactory. First, the 
terms imply that the water-content of the so-called meso- 
Pteridetum is higher than that of the so-called xero-Pteridetum ; 
but this is not established. Secondly, they imply that the 
members of the former association are “mesophytes ” and those 
of the latter association “ xerophytes”; but many characteristic 
members of the xero-Pteridetum can scarcely be admitted 
to the “ecological class” of xerophytes. Lastly, it is question- 
able if Schouw’s termination -etwm should be applied to any 
vegetation unit other than a plant association; and it is 
doubtful if the plant communities in question should be given 
a higher rank than that of ground societies. 
