342 MR. T. W. WOODHEAD ON THE 
and notwithstanding the deep shade of the latter the plant is 
still common. To the north-east humus is absent altogether 
the soil consisting of a clayey loam resting on stiff clay, becoming 
slightly more sandy, with humus in patches to the extreme east. 
In the stiff clayey soil the Bluebell distinctly thins out, and 
here it competes with Yellow Dead-nettle (Lamium Galeobdolon), 
Dog’s Mercury (Mercurialis perennis), and Arum maculatum, 
together with numerous root-branches of small trees, between 
which the bulbs of Scilla are often tightly packed, though they 
Fig. 5. 
AAAA Ter : 
NN floleus mellis. 
VV Deschempsia Reruosa, 
ee | 
Birks Woop. 
Map showing the distribution of Holcus mollis and Deschampsia flexuosa, 
not uncommonly escape this competition by penetrating more 
deeply in spite of the stiffness of the soil. Another deter- 
mining factor is the deep shade of the trees in this area, con- 
sisting of Beech, Elm, Sycamore, and Elder. The remainder of 
the wood to the north and west has a shallow sandy soil mixed 
with humus, there being little or no humus as a distinct layer 
on the surface, hence its power of holding water is greatly 
reduced. This soil lies immediately above a bed of Elland 
flagstone quarried at A and B (fig. 4). In this area Scilla only 
occurs in small straggling patches. Its chief competitor here 
