V. SUMMARY OF DISTRIBUTION. 229 



and recorded by other writers on British Botany. The letters and 

 figures used as abbreviations will be explained below, inuler their 

 respective heads or columns. The substitution of small horizontal 

 marks '- -' instead of letters and figures, indicates that no satisfactory 

 evidence has been found (or the occurrence of the species in the divi- 

 sions of the island to which such marks relate. The note of question ' ? ' 

 implies a doubt whether the alleged fact is sufficiently credit-worthy. 



1. Longitude. — In the 6rst column the letters 'we' stand for West 

 and East Britain, as explained on pages 136 — 138. A third letter 'i' 

 has been prefixed, in order to show the plants which extend westward 

 into Ireland ; and if set in the running type 'i' it indicates a doubtful 

 nativity of the species in that island. This part of the list may be less 

 correct than the rest; the plants of Ireland being less fully ascertained. 

 As authorities for their occurrence in the western island, Mackay's 

 Flora Hibernica and the Manual of British Botany hare been resorted 

 to, with some corrections of errors and misprints, chiefly supplied by the 

 Author of the Manual. The addition of Ireland, still more western 

 than West Britain, is intended as a partial equivalent for the absence of 

 a third longitudinal division in Britain itself; the form or figure of 

 which prevented more than a binary division. Columns of ternary 

 divisions were made by preference in the summary, because the inter- 

 position of an intermediate step in the series brings the extremes into 

 clearer contrast, and brings out also those gradations of difference which 

 cannot be so well exhibited by means of one single dividing line. (See 

 page 136). But a detached island, having much less extent in latitude, 

 is rather a leiip than a gradation in the ternary scries. A glance down 

 the column will show that, while the eastern and western floras of 

 Britain itself differ (mly by few species, the flora of Ireland wants many 

 of those which occur in West Britain, as well as almost all of those 

 which are absent from that side of the main island. The flora of 

 Ireland is less fully known ; and it seems likely enough that an 

 increased knowledge of Hibernian botany may lead to some of the pre- 

 sent blanks being filled in ; but it is in the highest degree probable, that 

 most of the Britis-h species so marked are truly absent from Ireland. 

 Those few found in Irejand, and absent from Britain, are enumerated 

 after the end of the summary. 



2. Latilude. — In the second column the letters *sm n' stand for 

 Smith, Middle, North ; the three latitudinal divisions of Britain ex- 

 plained on pages 134 — 5. It will be noted by the increased number of 



