Il] 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 (Lamium Galeobdolon), the dog's 

 mercury {Mercurialis perennis), the cuckoo-pint {Arum macu- 

 laturti), 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 fteamosa. 

 The latter species prefers an acidic, humous soil, where it is 

 associated with Galmm saxatile, Vaccinium, Myrtillus, Teucrium, 

 Scorodonia, and Solidago Virgaurea. 



The plant society in which the bracken {Pteris 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 -etum 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. 



