32 



going change, some species becoming extinct, from one cause or 

 another, others getting introduced, and after a time becoming 

 more or less naturalised. On this subject I 'will say more 

 presently. I pass on, therefore, to remark further that the extent 

 of a Flora of any district will depend upon the extent of country 

 "we include within that district. It is not uncommon with the 

 authors of Floras occasionally to strain the assigned limits, in 

 order to bring in some particular rare species found outside 

 them. This has been much done in the instance of the "Flora 

 Bathoniensis ; " such localities as Spye Park and BoAA'den being 

 often given, which are fifteen miles or more from Bath. If we 

 were to go the same distance in the opposite direction Ave might 

 take in a large portion of the Flora of Bristol. Perhaps as a fair 

 limit to our field we might assign ten miles as a distance not 

 ordinarily to be exceeded ; and if a few species of particular 

 interest or rarity occur outside those limits, but not far beyon<l 

 them, they might be inserted in an appendix. 



With these premises we may set the number of species in the 

 Bath Flora (excluding all the cryptogams except ferns), at from 

 700 to 760, according to the views we hold on the points above 

 mentioned. If to these Ave add about forty species discovered in 

 the district since the publication of the supplement to the " Flora 

 Bathoniensis,"* it Avill bring the number up to from 7J:0 to 800 

 accordingly. Suppose we take a middle term and call the 

 number 770. There Avill still be very many aiuongst these, 

 perhaps sixty or more, Avhich we cannot Avell leave out of our 

 list, but which probably, in some cases undoubtedly, oAve their 

 introduction into the neighbourhood to accidental causes. t I Avill 

 noAV mention some of the circumstances under Avhich such 

 introduction may take place. 



Sometimes these strangers are brought in Avith the seed soavu 

 in cultivated land, and where the conditions of the soil, &c., are 



* See Appendix. + See ditto. 



