30 TRANSACTIONS OF THE CANADIAN INSTITUTE. [Vot. VIII. 
but, from the shorter lapse of time, would have a more limited range 
than the older species. Thus, for illustration, Viola Selkirkii, Pursh, 
being common to Europe, Asia and America, is probably one of the older 
species, but being now rare on this continent, may presently be on the 
decline; Viola blanda, Willd, which is a frequent species of wide range, 
is doubtless about its maximum of energy; whilst Viola hastata, Mx., a 
third individual of the fifty species of violets now recognized in Canada, 
is uncommon, and may be either a recently formed species, or an older 
species on the decline. 
SPECIAL CAUSES OF DISTRIBUTION. 
Whilst there are general causes operating more or less in all countries 
which are now affecting the distribution of plants over Canada, there 
are numerous special causes arising from the relative influence on climate 
of great masses of land and of water; insular position, ocean currents, 
enormous sea coast lines, great or limited rain fall, the prevalence of fogs, 
the direction taken by chains of lofty mountains, the dryness of the at- 
mosphere in elevated situations, the great stretch of treeless prairie, 
the breadth and the cooling effects of the immense and deep inland lakes, 
the longer daylight in the summer months and the cooler nights, aid 
what might be termed the companionship among plants, all of which, 
in addition to the conditions which were at work in geological periods, 
now long past, have, each in its own area, among other causes, influenced 
the grouping of plants in different parts of Canada. 
In illustrating the effect of these forces in producing groups, it is 
impossible, where the area to be covered is so wide, to more than state 
the facts without going into details or discussing debatable points. 
Whilst in the Canadian Group the species are all of wide range, 
extending generally from the Atlantic to the Pacific, none are exclusively 
Canadian, but a large number have their maximum distribution in this 
country rather than in the United States. 
The species forming the Forest Group also occupy a wide area. 
That in the far west so many of these plants avoid the open prairies, 
is an illustration of what might be termed a companionship which nature 
has arranged between many of the smaller forms of plant life and their 
towering congeners, the trees, and which brings to light the dependence 
of the former and the protecting influence of the latter. Amidst the 
great bluffs of trees which margin the prairie, the general temperature 
is modified, the nights are warmer, the play of the sun’s rays on the smaller 
plants is more limited in extent and continues for a shorter time, the 
ground itself is more moist, and the high, drying winds of the prairies 
