1902. F R Am^R' —A ddiVmis ^0 /risk Topographical Bota7iy. 7 



dycerla Borrerl, Bab. 



12, Wexford.— S.W. corner of Wexford Harbour '01— C. P. Hurst 

 I.N., X., 255. 

 Bi*omus raccmosus, L. 



38. Down.— Rathfriland '00, Waddell— W.B.E.C. 1900-1. 

 Lastrea Thelypterls, Presl. 



23. Westmeath.— S.E. end of Iv. Owel '01— C. F. D'Arcy, /.M, x., 201. 

 Botrychlum Lunaria, Sw. 



19. Kii^DARE. — Prosperous '60— T. Cooke Trench. 



33. Fkrman. — Knockniore '01— W. West. 



As regards non-native plants, the usual variety of exotics of 

 various degrees of standing is reported. Also one or two 

 strange occurrences which the botanist may amuse himself 

 trying to explain^for instance, Cotoneaster 7nicrophyllat from 

 the Himalayas, growing over a rock by a tarn in among the 

 Nephin Beg range in Mayo, far from any house, road, or sign 

 of former cultivation ; or Cyclatnen sp., found in Newtown 

 Glen, near Lough Gill, Co. Sligo ! 



The last botanical contribution of the year is Mr. Colgan's 

 paper in the December number of this Journal. I have read 

 with much interest his remarks on floral diversity, my mind 

 having been working in the same groove on account of com- 

 parisons brought forth by the Table of Distribution of " Irish 

 Topographical Botany." While Mr. Colgan's ** index of floral 

 diversity " expresses the dissimilarity between two floras in 

 simpler terms than had occurred to me, I doubt whether for 

 most purposes of comparison the process has not been carried 

 rather far. If we wish merely to compare the amount of 

 diversity of flora between two areas, his " index " is sufiicient : 

 it means — of the total flora of the two areas, so-ajid-so percent, 

 occurs in one or other, 7iot in both. But this statement is sure 

 to raise the questions — how many of this so-and-so per cent, 

 are confined to area A, how many to area B, and what is the 

 relation of each to the total flora of each, and to the number 

 of plants common to both ? All these facts were ex- 

 pressed in the original fraction, but have been eliminated 

 by (i) adding together the two constituents of the nume- 

 rator, and (2) substituting a decimal for the actual 

 denominator. An example from Mr. Colgan's paper 

 will make my meaning clear. Antrim and South Kerry 

 (total floras 777 and 680 species respectively) have 602 species 

 in common, 175 peculiar to Antrim, 78 peculiar to South 



