[Vor. XXXIX. 
Within its limits, 
the plants have a wider range of habitats, attain a greater size, 
It is also shown that. 
In a former paper the writer 
THE AMERICAN NATURALIST. 
(103) pointed out that if the distribution of the characteristic 
bog plants be plotted on a map, the Laurentian region of Canada 
is indicated as their center of distribution. 
and are more abundant than elsewhere. 
dispersal for the fauna and flora. 
876 

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‚the bog 
plants range 
f hi 
persal 
Dr. P. A. Rydberg, 
8e, while the herbaceous 
1S 
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XICO, 
canadensis, Acer Bennsylvanicum, Betula papy- 
ssor Aven Nelson, 
bligations to Profe 
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IC seas to the Gulf of Me 
. 
species are most limited in extent of d 
rifera, Prunus Pennsylvanica, 
center. The writer is under o 
ave a wider ran 
Fic. 2.— Map showing distribution of Picea 
and Mr. W. P. Holt for 

the tree 
shrubs h 
from the Arct 
