44 n. INEQUALITY OF SPECIES. 



here to the uncertain limits of genera is somewhat inter- 

 ruptive of our onward course ; although it is but a fur- ' 

 ther illustration of the like impediment in the way of 

 phyto-geographical expositions, as that arising from the 

 uncertain limits of and between species. 



4. Inequality of Species. 



Intimately connected with the uncertainties in the cha- 

 racters, and Hmits of species, comes another inconve- 

 nience to the phyto-geographer. Among the species of 

 Britain, as now named and described in books, there is 

 seen much the same sort of inequality or non-equivalence, 

 as was before shown to be the case with the ordinal 

 groups of systematic botany, and more briefly asserted of 

 generic groups. It may be said that some species stand 

 out clear and distinct, and are rarely or never confused 

 with aught else, — at any rate, not with aught else in 

 Britain ; also that they have thus existed for some cen- 

 turies, and in all likelihood during many centuries. If 

 they sport into varieties, the most reckless " describers of 

 specimens " do not venture to ti'eat the casual varieties of 

 these plants as species. Thus stand out the single or few 

 native species oi Bellis, Linntea, Parnassia, Trientalis, 

 Adoxa, Calluna, Andromeda, Clematis, Myrica, Tamus, 

 Paris, Myosurus, Chrysosplenium, Cornus, Rhamnus, Tri- 

 glochin, Scilla, Lythrum, Limim, Astragalus, Convolvidus, 

 Vaccinium, &c. It is true, however, that the species of 

 several of these genera cannot be held thus clear and cer- 

 tain when our scope extends beyond Britain. But, even 

 in this wider view, we should oiil}^ require to substitute 

 the names of other non-British genera, in place of those 

 so altered or affected. The fact would remain the same, 

 though exemj^lified differently, that there are plants 



