ROBERT SMITH ON PLANT ASSOCIATIONS OF THE TAY BASIN. 201 
Alpine ridges of the Grampians dwarf willows, mountain azalea, 
Potentilla Sibbaldi^ etc., have the ground at their own disposal. In 
the waste grounds of the lower part of the basin whin, broom, sloe, 
rasp, rose, etc., may each form societies. 
III. — Grasses play an important part in carpeting the soil from 
the property they have of forming turf, especially when mown or 
eaten down by grazing animals. Their societies are best developed 
on the moister parts of the hills, although Nardus stricta can be 
found on the worst and driest soils. Agrostis vulgaris^ Deschampsia 
ccBspitosa^ D. flexuosa^ Fesiuca ovina^ and Phalaris arundinacea^ are 
amongst the best marked species. Lolium perenne is the social 
species of the hayfield, but rapidly disappears when the soil is 
allowed to lapse from cultivation. 
IV. — On the cold moist earth and in the marshes Sedges ( Carex, 
Scirptis, Eriophorum^ etc.) largely take the place of grasses. 
V. —Certain Rushes, e.g., Juncus squarrosus on peaty soil and 
J, mnmunis in the marshes. 
VI. —Amongst Herbs, the social species are especially those 
whose broad leaves can effectually shut out light from intruders, 
and whose rhizomes usurp most of the ground. No better examples 
can be given than Petasites and Tussilago. 
VII. - —Ferns tend to live socially, especially the bracken (Pteris 
aquilina)^ in woods and on well-drained hillsides. The male fern 
(Lastrcea Filix-mas) often forms a sub-society under the shade of 
trees. 
VIII. —Of the Mosses, Sphagnum plays the most important part 
as a social species; the remains of its great societies form peat. 
IX. —Only a few Lichens cover much ground, although many 
form small societies. Cladonia rangiperina on our moors, and 
Cetraria islandica on the alpine plateaux, are the best marked forms. 
Besides these groups of social species one must mention three 
others which are much more dependent for their sociability on the 
environmental conditions. 
X. —Aquatic Plants. —Here are included such societies as that 
of Elodea^ which has of late choked so many canals and ponds, 
Chara^ Pota 77 iogeton, Ny 77 iphcca^ etc. Each of these depends primarily 
on the constant presence of water.* 
XI. —Marine Plants. —Salt and water are here the necessary 
conditions. Zostera is our only species from amongst the flowering 
* For many interesting observations on the societies of aquatic plants one 
should consult the papers by M. Magnin on “The Vegetation of the Lakes of 
the Jura Mountains.” 
