SOMMERS FLORA OF NOVA SCOTIA AND COLORADO. 123 



admirable report of the U. S. Geological and Geographical Survey 

 of the Territories, by Dr. F. V. Hayden, I was deeply interested 

 in finding described there many species identical with those of our 

 Provincial flora. 



I was therefore led to institute a comparison between these floras, 

 for which purpose I prepared a list of Provincial species, making it 

 as complete as circumstances would permit ; contrasting this latter 

 with the synopsis, I was enabled to observe the amount of corres- 

 pondence between them ; this, in its result served to reveal a much 

 closer alliance than a casual study seemed to show, a circumstance 

 which induced me to bring the subject before the Institute. 



Inasmuch as the Coloradian Flora presents us with many truly 

 boreal species and a few maritime plants indigenous to our locality, 

 whose origin, so far as we are enabled to understand it, has been in 

 the northern portion of our continent, we are led thereby to a con- 

 sideration of their migration thither. 



Considering the respective localities of the two regions, we find 

 a difference which is in favor of Colorado ; its geographical position 

 may be roughly stated as being on the thirty eighth degree of north 

 latitude, while that of Nova Scotia is on the forty-fifth, or a variation 

 of seven degrees, sufficient on this side of the continent to produce 

 that diversity of climatic conditions which exists between Nova 

 Scotia and those Middle States that lie under the same degree of 

 latitude as Colorado. 



As these conditions influence plant life very materially, since we 

 find the Middle States Flora deviating considerably from our own, 

 how much more would we expect finding a wider variation in the 

 flora of a region so far to the west of us, which from this latter 

 circumstance had its difference of climate increased by that pecu- 

 liarity of the isotherms or heat lines seeking on this continent a much 

 higher latitutude on its western side than that which they occupy 

 to the east ; the isotherm of Nova Scotia, ' ' speaking without book " 

 finding its western extremity some ten or fifteen degrees north of it, 

 that of Colorado arising very far south of it on our side of the Con- 

 tinent. This phenomenon presenting to us a very wide departure 

 between the mean annual temperatures of regions situated directly 



