126 SOMMERS — FLORA OF NOVA SCOTIA AND COLORADO. 



toward that portion of the continent which afforded the conditions 

 for support. 



Following the gradual withdrawal of the ice the face of the con- 

 tinent assuming more or less the condition which it now presents, 

 had time to rehabilitate itself. Our northern species being pushed 

 out by the southern forms which aided by the increasing heat began 

 to dispute the possession of the soil forcing them to migrate north- 

 ward. But not alone to this process may we attribute the reappear- 

 ance of plant life in the northern portion of our continent, we must 

 recollect that through the various stages of the glacial period, many 

 species or individuals of species previous to their demise, had 

 deposited germs ; these from adverse circumstances, being unable to 

 germinate, would remain imbedded in the drift, and recollecting 

 property which many such possess of retaining their germinating 

 power for lengthened periods, even under adverse conditions, ob- 

 serving as we may the immunity of the innumerable germs scattered 

 over our soil annually, from the effects of our rigorous winters, 

 we can easily assume that the conditions which the drift afforded for 

 the preservation and dissemination of those germs were not more 

 unfavorable than that of a lengthened hybernation. 



Hence we find the southern part of our continent supporting in 

 their elevated positions species not found in the intervening plains 

 and valleys, but having their true habitat in our northern regions, 

 they, no doubt are boreal forms driven south in a former age, when 

 the conditions necessary to existence were denied them in their own 

 regions, otherwise they may have sprung from germs transported 

 with the drift, and germinating in favorable situations. Either way 

 the hypotheses started, may, in a measure, account for the corres- 

 pondence which the list here annexed exhibits. 



List of Species and allied genera,* common alike to Nova 

 Scotia and Colorado : 



JRanunculacecB. 



Clematus, Virginiana. Linn. 

 Thalictrum, cornuti. Linn. 



Anemone, Pennsylvania. L. 



Ranunculus, aquatilis. L. 



R. Flarumula. Var reptans. Gr. 



*Genera having closely related species indigenous east, though not Nova Scotian as 

 ar as is known. 



