British North American Plants. ie 
The following species sufficiently indicate the group :— 
Viola rostrata, Pursh. Conopholis Americana, Wall. 
Ceanothus ovalis, Bigel. Pentstemon pubescens, Sol. 
Staphyllea trifolia, L. Lophanthus nepetoides, Benth. 
Desmodium cuspidatum, T. & G. Gentiana alba, Muhi. 
Lespedeza hirta, Ell. Asclepias phytolaccoides, Pursh.. 
Aster ericoides, L. Montelia tamarascina, Gr. 
Lobelia syphilitica, L. Phytolacca decandra, L. 
Vaccinium stamineum, L. Quercus castanea. Muhl. 
A number of representatives of this group, including 
such plants as Coreopsis verticillata, L., C. lanceolata. L., 
Cacalia tuberosa, Nutt., Calamizntha Nuttallia, Benth., and 
Scutelaria versicolor, Nutt., are limited to the vicinity of 
Lakes Huron and Erie, some extending even to Lake 
Superior. In the United States, their range is similarly 
confined to Wisconsin, Illinois, Pennsylvania and south- 
ward, It is difficult to give a reason for this. The sugges- 
tion which I have already made that, in geological time each 
species has had its initial, its maximum and its final stage 
of existence as a species, will, however, I think, explain 
numerous eccentricities in range everywhere, Whilst many 
plants, at the present time, are at their maximum stages of 
activity in individual growth and in reproduction, and have 
now their maximum breadth of distribution, some are merely 
in the early or initial stages of this activity, and at the 
initial points of their ultimate area of range, whilst others 
must be on the decline when activity in reproducing the 
species is lessening and the area of distribution is being 
circumscribed. The range of each species is thus vastly 
affected. When the stage of decline has been reached, 
climatal and other causes which would in the ordinary 
course limit range, would have greater effects on the species 
than upon others which were in the progressive stage of 
activity or had reached the maximum. 
In these modern times, cultivation itself is having a 
limiting effect on the distribution of plants as well as 
animals. The yearly extension of the cultivation of the 
soil, the demands of commerce, the enlargement of towns 
and cities, and forest and prairie fires, all contribute annually 
to this result, 
