INTRODUCTORY EXPLANATIONS. 9 



degi-ee, in order to render such notices clearly intelligible 

 to any botanists who may have hitherto given little of their 

 attention to the subject of geographical botany. 



The indigenous and natmalised British plants amount to 

 fourteen or fifteen hundred species. Let it be supposed 

 that some patiently industrious botanist takes an equal 

 number of maps of Britain, in which the boundaries of 

 coimties are traced, but all else is left blank. Devoting a 

 map to each species, he enters on the map the name of 

 every county in which he has seen the species himself, or 

 has been informed that it grows. He then compares his 

 maps together, and finds the utmost inequality in the dis- 

 tribution of the species, as indicated by the names on his 

 maps. Several of the maps are still left wholly blank, with 

 the exception of some single county on each ; as, for ex- 

 ample, those devoted to Cynodon Dactylon and Antheri- 

 cum serotinum. In other maps, the names of two coun- 

 ties will appear ; as in those for Erica ciharis and Astra- 

 galus alpinus. In some of them, there will be three coun- 

 ties named, as in those for Gentiana nivalis and Saxifraga 

 rivulai-is. And it is not unlikely that such instances might 

 be found, showing every successive number fi"om one 

 county up to fifty or sixty counties. But om* botanist, thus 

 at work, would find none of his maps with more than fifty 

 or sixty counties marked on them, vmless his own indivi- 

 dual investigations had extended through the many comi- 

 ties, for wliich we still want Floras, or lists of theii* more 

 common species. Could om- libraries supply him with lists 

 of species, the common equally as the rare, for every single 

 county, it is probable that he would then find about two 

 himdred species reported in aU the eight} -two or eighty- 

 three counties of Britain. Some species would then ajj- 

 pear to be absent from one county only, others from two 



c 



