Marsh , and its Relations to Evaporation , &c. 277 
first deal with the various types of plant form, and then with the stratifica- 
tion of the vegetation as a whole. 
Now even in the case of those plants which reach the upper surface of 
the vegetation, all do not develop their leaves at the same vertical level. It 
has long been known that rhythmic variations in the size of parts occur 
during the development of the shoots of flowering plants. Thus in ascend- 
ing a shoot formed during one vegetative season not only do the internodes 
show a successive increase and decrease in length, but the leaves also 
exhibit similar changes of dimensions. 1 The shoots of different species, 
however, show marked differences with respect to the relative positions on 
the stem at which the maximum size of leaf is attained. In some of the 
plants under consideration, the largest leaves are formed near the base 
of the stem, and their subsequent diminution in size is somewhat abrupt. 
In others the rise and fall in the size of successive leaves is gradual. In yet 
others the maximum leaf size is only attained at comparatively high levels 
in the vegetation. Again, while in many cases the greatest leaf-develop- 
ment occurs on the erect flowering shoots, in others the larger leaves are 
chiefly formed on lateral stolons, &c., and thus are practically radical 
in position. A rough classification of the plants in question according to 
their ecological habit, 2 may perhaps conduce to clearness. But it must be 
remembered that the varieties of plant form outlined below are not sharply 
demarcated. There is, in fact, every gradation between the different 
types : — 
Type (1). The whole plant is more or less dwarf, and is generally 
found in sheltered situations. If growing with taller plants, it forms 
a constituent of one of the lower layers of the vegetation. The inflore- 
scences or sporophylls are frequently inconspicuous ; e. g. Hydrocotyle 
vulgaris 3 (cf. Text-figs. 2, 4, and 6), Lastrea Thelypteris , Ophioglossum 
vulgatum (Text-fig. 6), &c. Various mosses and liverworts may also 
be included here. The following have conspicuous inflorescences, and 
form a transition to type ( 2 ), Orchis incarnata , Epipactis palustris, Potentilla 
sylvestris, Menyanthes trifoliata^ and Caltha palustris. N.B. The two latter 
are but rarely found in the shade of other plants. 
Type ( 2 ). The plants are frequently taller : their inflorescences more 
or less reach the general vegetation level, or even project beyond it. The 
leaves, however, are chiefly developed in comparatively low layers of 
the vegetation, and markedly decrease in size (sometimes abruptly) as the 
upper layers are reached; e. g. Valeriana dioica (Text-fig. 1), Car dims 
pratensis , Samolus Valerandi , Scabiosa Succisa (Text-fig. 6), Angelica 
1 Cf. Pfeffer (’ 03 ), p. 7 ; also Groom (’ 08 ), p. 98. Pfeffer states that ‘the variation in the size 
of leaves was known from Goethe onwards ’. 
2 This refers to the aerial shoots only. In Yapp (’ 08 ), p. 69, will be found a list in which 
these same plants are arranged according to the degree of soil moisture preferred. 
3 The plant names used in this paper are those employed in Yapp, l.c., pp. 69-70. 
U 2 
