616 X. GENERAL REMARKS. 



group of more generally diffused species among which 

 they occur, hy the partial sites and limitations either of 

 their whole areas or of their centres of greatest fre- 

 quencj"-, along with the direction of their decrease or 

 attenuation. 



The same might be done also with the flora of Middle 

 Europe, between the Mediterranean and Baltic seas. In 

 addition to the generally distributed species, which are 

 spread somewhat continuously from coast to coast, there 

 is the large group of alpine species mingled with such of 

 the more general species as are found to ascend to con- 

 siderable elevations on the great mountains. There are 

 also plants of the Mediterranean, Atlantic, and Baltic 

 coasts, and others spreading away from those coasts more 

 or less far inland ; some of them meeting and crossing 

 each other in their different directions of attenuation and 

 successive cessation. And along with the genei'al species 

 that extend far eastward, there occur also yet other spe- 

 cies which are wanting near the oceanic coasts ; while in 

 turn many of the occidental species are absent from the 

 tracts where those oriental species are most j^revalent or 

 exclusively found. These are so many different types or 

 characters of distribution. 



On looking to Europe at large, as one whole area, cer- 

 tain general sj)ecies are still found to be spread over aU 

 or much of this wide space, from North Russia and 

 Sweden — some even from Lapland — southward to Spain, 

 Italy, and Turkey. Mingled with these in the north, 

 there are also truly boreal species which decrease in their 

 abundance and successively cease southward. Many 

 austral species in turn may be traced in the northerly 

 direction, gradually decreasing in their abundance or 

 frequency, and successively ceasing. So also are there 

 various occidental and oriental species sjoreading in like 



