British North American Plants. 3 
plant, has its birth in the swelling seed, its maturity when 
it expands its flower, and its death when, after ripening its 
seeds, it withers and decays. amie each species has 
had its beginning, in past ages, in the development and 
permanency of a well defined variety formed from at 
already existing spevies. This new species, thus formed, 
would, in the course of downward geological time, reach its 
highest stage of existence as a species,—its period of most 
active growth and of largest area of distribution, when its 
ability, under further new conditions, to give rise to fur- 
ther new species, is greatest. Finally, such species has, in 
after geological time, its period of decline, when the activity 
of its individuals is gradually lessened and its area of distri- 
bution diminished, until extinction comes, leaving to the 
palzobotanist the duty of revealing its story when he dis- _ 
covers the remains in the clay nodule or the hardened rock. 
Applying this idea, the older existing species, which are at 
their maximum of activity, would, with the greater oppor- 
tunities which in time they had had, have naturally a wider 
range, under the same set of circumstances, than those which 
were of more recent creation. Others, again, of the older 
species, would have passed their maximum of energy and, 
even though wide of range, would, in each passing century, 
become more rare. The species of newer creation would, 
on the other hand, be gradually extending their range . 
wherever circumstances of climate and situation admitted, 
. 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 Hurope 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 Vivsla hastata, Mx., which is uncommon, may be 
either a recently formed species, or an older species on the 
decline. 
The same idea can be equally well applied in the case of 
animals. 
