NATURAL HISTORY SOCIETY OF GLASGOW. 19 



veneris and Hordcum murinum are both common plants in England; 



the former an annual weed in every corn-field, the latter a wayside 



grass. How does it happen that both of these plants penetrate 



into Scotland on the east coast and not on the west 1 Latitude 



would appear to have nothing to do with it, for the small difference 



that is between the latitude of Ayrshire and East Lothian is in 



favour of the former, and the climate of the west coast is milder 



than that of the east, the cold east winds being neither so frequent 



nor so severe. All these taken together, should, one would think, 



be in favour of such plants penetrating farther north on the west 



than on the east side of our island; but the very reverse is the 



truth. Can it be possible that these plants, having nearly reached 



their utmost northern limit, are arrested in their farther progress 



by such apparently trifling impediments as the Solway on the one 



side and the Forth on the other 1 Hwdeum mnrinum is not found 



in Ayrshire, although it is common all along the south side of the 



Firth of Forth, and forms a large proportion of the vegetation on 



the Calton Hill at Edinburgh, which appears to be about its 



northern limit in the east. We are almost forced to believe that 



these two arms of the sea, penetrating into the very centre of the 



island — one on the east, and the other on the west — form a 



sufficient barrier to prevent their farther progress northward. 



Malva Sylvestris, Knautia arvensis, Silene inflata, etc., all al^ound in 



the Lothians, but occur only sporadically in the west, and other 



species of the genus Silene, as nutans, noctiflora, and conica, are, 



as regards Scotland, confined to East Lothian alone. Carduus 



tenuiflorus abounds along the Firth of Forth, but you will look 



for it in vain along the Firth of Clyde. As a set-oflF against 



this, we have Cotyledon Umbilicus plentiful on the shores of the 



Clyde, but whoUy unknown in the east. Why does this plant 



abound on Ailsa Craig, while it is not to be found on the Bassl Why 



does it frequent every crevice in the cliffs of Culzean, and yet refuses 



to grow on the cliffs of Tantallan'? These are questions much 



easier asked than answered. An eastern exposure will not account 



for it, because it is common enough on the east coast of Ireland. 



Again, in the east every wheat-field is gay with Papaver Elmas, a 



species all but unknown in the west, where its place is usurped by 



a nearly allied species, P. duhlum, which is as rare in the east as the 



other is in the west. I have been astonished, when in the Lothians, 



where so much care is bestowed in keeping the fields clear of 



