Geographical Distribution of Indigenous Plants. 59 
Carex teretiuscula. 
Carex teretiuscula, var. major. 
Carex chordorhiza. 
Carex tenuiflora. 
Carex stellulata. 
Carex tenella. 
Carex vulgaris. 
Carex aquitilis. 
Carex limosa. 
‘Carex irrigua. 
Carex alpina. 
Carex livida. 
Carex panicea. 
Carex panicea, var. refracta. 
Carex pallescens. 
Carex capillaris. 
Carex flava. 
Carex viridula. 
Carex filiformis. 
Carex aristata. 
Carex pseudo-cyperus. 
Carex miliaris. 
Carex rariflora. 
Agrostis vulgaris. 
Agrostis alba. 
Cinna arundinacea, var. pendula. 
Calamagrostis stricta. | 
Calamagrostis langsdorffi. 
Calamagrostis lapponicum. 
Calamagrostis arenaria. 
Keeleria cristata. 
Poa annua. 
Poa compressa. 
Poa alpina. 
Poa cesia. 
Poa serotina. 
Poa pratensis. 
Triticum repens. 
Triticum caninum. 
Elymus sibericus. 
Aira ceespitosa. 
Aira flexuosa. 
Hierochloa borealis. 
Triticum subspicatum, var. molle. 
Phalaris arundinacea. 
Millium effusum. 
The distribution of some of these requires a little explanation. Of 
the following none are known to pass to the north of latitude 50 deg. 
in this country, though they are found as far north as 70 deg. in 
Europe. 
Ranunculus repens. 
~ Oxalis acetosella. 
Vicia cracca. 
Geum rivale. 
Geum strictum. 
Geranium robertianum. 
Veronica officinalis. 
Atriplex patula. 
Juncus stygius. 
Cyperus flavescens. 
Microstylis monophyllos. 
Humulus lupulus. 
Millium effusum. 
This apparently anomalous distribution will be explained when we 
find that the isothermal line of 40 deg. Fahr. passes a little to the 
south of latitude 50 deg. in North America, and a little to the south 
of latitude 70 deg. in Europe. It may, therefore, well be that the 
temperature of this country is not now high enough to allow these 
plants to pass the 50th deg ; and it is reasonable to suppose that when 
it was milder the species lived as far north as in Europe. 
The true Betula alba extends into the Arctic regions in Europe. 
Our representative of the species, the variety populifolia, is not found . 
north of latitude 46 deg. We may, therefore, say that our variety is a 
southern form, the ancestor of which, at a former period of time, lived 
in the far north, but owing to an increase of cold it has become ex- 
tinct, leaving the variety as its southern representative. So, too, 
with Taxus baccata, var. canadensis. Our variety is probably the 
