154 JOHN MACOUN ON CANADIAN POLYPETALZÆ. 
the south, weakness and eventually extinction. Hence a southern dispersion is a destruc- 
tive one. Species weakened by a southern migration can never return ; and, in examining 
our fossil or living floras, we find that species, when once displaced, never re-occupy the 
vacated district by areturn from the south. When I say weakened, I mean that the species 
become so changed by heat that it is unable to resist the cold of its old habitat. Examples 
by the score might be given of plants which have lost their power of resistance to the cold 
by being cultivated in a more equable climate. 
2. Many years since, Edward Forbes propounded the theory of “Centres of Creation,” 
and Sir Charles Lyell and Mr. Darwin, both held views that were in accord with Forbes. 
My view is that our flora originated far to the north—was, in fact, circumpolar—and 
descended on longitudinal lines to the south before the advancing cold of the glacial epoch. 
This view harmonizes with the distribution of our own flora, and shows why our eastern 
species have so little in common with Greenland, while the western shores are largely 
clothed with Asiatic species, and the Rocky Mountains present no barrier to western exten- 
sion. The survival of the fittest is well seen in the adaptability of these new arrivals to 
their changed conditions. Whether we are believers in natural selection or not, we can 
see a few types, by the operation of these or other laws, becoming an innumerable army, 
and actually taking possession of the whole land—sweeping the old flora out of exist- 
ence, or pressing it more to the south, or isolating it, as we believe is the case with 
the big trees of California. This is clearly shown by the following table. 
3. The six leading orders of the Polypetalæ in our flora are :— 


Ranuneulaceæirereecec-ercre-er 78 30 2 
Duibedecononaonootunnstonsodess 97 41 0 
Caryopbyllacere:jecireit ster eel) «ele 67 37 0 
DÉPUMIDORE eee ee eee 135 17 5 
INGER Os ES Eee rer ere 105 37 10 
Saxairapacere Ho ogpa 000 00000000 76 31 0 
MOEN) Soncocu sandasioagonn so00dn 563 193 17 






The whole flora consists of 900 species and 47 orders, yet in these six orders we have 
no less than 563 species, or nearly three-fifths of the whole. Those which pass beyond the 
Arctic circle number 230 species, and of these six orders 198, or within 37 of the whole 
number. In Miocene times only seventeen species of these orders left a record in the 
rocks, and I note this as one reason why I believe them to be the newer, if not the newest, 
types of creation. 
It is singular that these orders are easily distinguished and stand out from all others 
by distinctive characters, which plainly separate them from other orders. But within the 
orders themselves genera and species are unstable, and varietal forms are almost as numer- 
ous as species and generic differences, I might say, are at the will of the systematist. Now, 
here are five types of vegetation which are eminently Arctic, eminently vigorous, and 
pre-eminently varietal, and are at the present time in our flora fulfilling all the condi- 

