240 SOMMERS — NOVA SCOTIA COMPOSITE, — ASTERS. 



title, which includes the whole group, as is done by Prof. Gray in 

 his Manual, in which priority is given to the Linnasan term Isevis, 

 the others representing varieties under this head. 



Circumstances like the above are more or less characteristic of 

 all the native species which I have so far examined. I have con- 

 cluded, therefore, that all well-defined species, — or perhaps I should 

 say true species, — must be looked upon as so many groups, vary- 

 ing individually, yet possessing within each group certain character* 

 istic peculiarities, which, being common to members of each, are 

 sufficient to relegate them from the members of other groups. 



I am inclined also to the opinion, " the correctness of which I 

 leave for future determination," that more species are described 

 than have an existence in nature. Observations prove that when 

 passing from the generic diagnosis of the asters, We have, on the 

 whole, few genuine and really natural specific characteristics separ- 

 ating its members. 



. The difficulty of marking the dividing lines between species in 

 this group of plants arises from their inherent plasticity. Of 

 all feral plants, they have the greater tendency to vary in their 

 natural positions ; apparently the slightest change in their physical 

 surroundings tends to produce changes in form, which, though not 

 sufficiently marked to furnish specific distinctions, are yet perplex- 

 ing enough to severely tax the diagnostic skill of the Botanist who 

 attempts to separate them. 



Having on many occasions experienced this difficulty, I have in 

 the following notes attempted to characterise such of our 

 native asters as appear to possess definitive specific peculiarities, 

 and have in the case of each endeavored to relegale them to the group 

 or species described in the Class Btok. In this attempt I have 

 relied principally upon the character of the achamia, pappus, and 

 scales of involucrum, and upon the inflorescence, leaves and axis 

 when admissible, the former being in general more reliable for 

 distinctive diagnosis, the latter not so reliable, since, in the very 

 many cases their characteristics are so indefinite as to prove perplex- 

 ing and abortive as distinctive evidence of specific difference. 



The labor may, after all, prove to be a work of supererogation ; 



