28 i 
Marsh , and its Relations to Evaporation , d?V. 
Thus the general vegetation of the Fen is made up of a number 
of species of very varied ecological habit. Although the distribution of 
these species depends to a great extent on the relative dampness of the 
soil, 1 this factor alone will not account for the preferences of the plants in 
all cases. For instance, certain species are rarely found in the denser 
mixed vegetation of the marsh, even when the moisture conditions are 
apparently suitable. These seem to prefer the more open banks of ditches 
or streams. Such are Caltha palustris , Epilobium hirsutum , Samolus 
Valerandi , &c. 
From what has tfeen said above, of the habits of the different species, 
it will be seen that where the vegetation is rank and dense, marked stratifi- 
cation (at least of the transpiring organs) will occur. Although such strata 
are more obvious in woodland than in other formations, yet they are found 
to a greater or less extent in most vegetation. Warming, 2 in fact, says 
that layers may be distinguished in every plant association. Clements, 
however, does not appear to recognize the existence of stratification in his 
6 co-ordinate associations \ In the latter, with which he classes most grass- 
land and herbaceous formations, ‘the individuals are on the same level, 
or nearly so. 5 3 
In the mixed vegetation under consideration the number and com- 
position of the strata vary according to the species present, the height of 
the vegetation, the season of the year, &c. Moreover, the different strata 
shade into each other more, and are in consequence less distinct than those 
of a forest. The following, however, shows the kind of stratification which 
may be observed (cf. Text-figs. 4 and 6) : — 
(a) The ground or bottom stratum consists of liverworts and mosses, 
and the young seedlings of many plants. 
(b) The next stratum will contain the lower parts of the leaves of 
Carices and other plants of type (5). Also the taller young plants, Hydro- 
cotyle and Ophioglossum ; the larger leaves of Orchis incarnata , Valeriana 
dioica , Scabiosa Succisa, Carduus pratensis , & c. ; the lower leaves (formed 
in springtime) of many plants, e. g. Spiraea Ulmaria . 
(e) A still higher stratum will comprise the middle portions of the 
grass and sedge leaves ; Lastrea Thelypteris ; the larger leaves of such 
plants as Angelica sy Ives Iris, Peucedanum pains tre , Thalictrum flavum , 
Spiraea Ulmaria , Symphytum officinale, &c. Also the inflorescences of 
a few species, e. g. Orchis incarnata. 
(d) The surface stratum contains the upper parts of the leaves of the 
sedge type ; many of the larger cauline leaves of Lysimachia vulgaris, 
Lythrum Salicaria, Phragmites communis, &c. ; the smaller cauline leaves 
of Spiraea Ulmaria , Thalictrum flavum , &c. Also the inflorescences of 
many plants. 
1 Yapp, 1. c., pp. 68 et seq. 
2 Warming (’96), p. 1 1 7. 
3 Clements (’05), pp. 206-7. 
