388 MR. T. W. WOODHEAD ON THE 
In these different situations the plant varies much in size. 
Typically from one to two feet in height, it may, in exposed 
windy situations and in a shallow soil deficient in humus, be not 
more than two to three inches in height, as on the western grassy 
slopes of Meltham Cop and at Cheese Gate Nab. Here the 
stem is much branched, very thin and wiry, and the cuticle of 
the epidermis much thieker than that of the taller larger plants. 
The internodes are greatly reduced, and in consequence the 
leaves, though very small (3 X4 inch), become much crowded 
together, so offering mutual protection. This dwarf form is of 
frequent occurrence in places where the soil is relatively dry 
and deficient in humus. Schröter (84) figures similar differences 
in V. Vitis-idea and V. uliginosum, the small-leaved form of the 
latter species having received the name var. microphyllum. 
Plants growing in very exposed situations frequently develop 
brown or red pigments, which, as Kerner (52) and others have 
pointed out, is a common feature in leaves exposed to cold 
and intense light. Overton (76) has shown that these red 
pigments were produced under the influence of cold ; and Stahl 
(91) previously made the interesting observation that portions 
of leaves containing such pigments had, when illuminated, a 
higher temperature than parts not so coloured ; and Rathay (80), 
Wiesner (104), and others have shown that transpiration is 
less in red than in green leaves. This sequence of events is 
interesting: that cold produces in leaves pigments which, under 
the influence of light, occasion compensatory warmth, and such 
leaves have also a reduced transpiration, all features of great 
value to a plant exposed to xerophytie conditions. In different 
species these pigments are produced under various, even opposite 
conditions, as shown by Katié (51), to whose paper, also to 
Busealioni & Pollaeei (11) and Czapek (21), reference may be 
made for literature and full consideration of the subject. 
Fig. 56 shows a transverse section of a leaf of the high 
Moorland-form ; the epidermis is strongly cuticularized, and the 
double row of palisade-cells well developed, the upper ones being 
much elongated and occupying nearly half the thickness of the 
leaf. Stomata are abundant on the under surface, but very few 
on the upper surface, and here they occur chiefly in the neighbour- 
hood ofthe veins. In extreme forms from very exposed, sunny 
and dry situations no stomata were found on the upper surface, 
wbile they were numerous on both surfaces in the shade-forms. 
