334 MR. T. W. WOODHEAD ON THE 
which had to be omitted altogether or only slightly dealt with 
in the primary surveys, and thus determine whether more 
detailed work would lead to profitable results. While the object 
of the primary survey was to illustrate the chief plant associations, 
the present paper rather attempts to bring out the dominant 
factors affecting the distribution and modifications of a limited 
number of the commonest species which form the undergrowth 
of our woodlands. The distribution of these has been traced in 
the uneultivated areas of a small portion of the West Riding of 
Yorkshire to the South and West of Huddersfield, a district 
ineluded in the Survey by Smith & Moss (Leeds & Halifax 
District), and reference should be made to this for a general 
account of the vegetation of the district. 
The area selected is favourable in that it affords considerable 
variation in altitude (1700 to 250 feet), in rainfall (50 to 32 
inches), in temperature (42? F. to 47°5 F.), in exposure to pre- 
vailing winds, in soil conditions—e. g., deep ill-drained peat, 
shallow, relatively dry peat, humus, and soils derived from the 
denudation of coarse millstone-grit, fine-grained coal-measure 
sandstones, shales, and clays; and hence there are considerable 
differences in available water and inorganic salts for plant-food. 
The study also throws light on the changes that have occurred 
in the vegetation of the district as a result of altered conditions. 
The problems to be considered therefore were the investigation 
of the conditions affecting the distribution of the common plants 
of the undergrowth with reference to soil, moisture, exposure to 
wind, light, and shade, and to compare the tissues of the several 
species occurring under these various conditions. The species 
examined included, among others: Bracken (Pteris aquilima, 
Linn.), Bluebell (Scilla festalis, Salisb.), Quick or Creeping Soft 
Grass (Holcus mollis, Linn.), Wavy Hair-Grass (Deschampsia 
flecuosa, Trin.), Bilberry (Vaccinium Myrtillus, Linn.), Dog’s 
Mercury (Mercurialis perennis, Linn.), Yellow Dead-nettle 
(Lamium Galeobdolon, Crantz), and Hog-weed or Cow-Parsnip 
(Heracleum Sphondylium, Linn.). 
A very considerable amount of detailed work remains to be 
done in every branch of the subject, especially with regard to 
soils. The observations here recorded can, therefore, only be 
regarded as preliminary to more extensive work ; and it 1s also 
important that similar examinations should be made of other 
selected areas and compared, for it is only by such comparisons 
that we can hope to arrive at the most satisfactory results. 
