X1V FLORA ORCADENSIS. 
recesses, gullies, and corries, and its Meadow of the 
Kame, forming a well-sheltered area with interesting 
gorges leading to the higher grounds. The most 
noteworthy hill is the Ward, Hoy, rising to 1565 
feet, with its hammars—exposed rocky ledges—about 
half-way up, or probably a little less. The hills and 
sheltered valleys in Walls are also botanically inter- 
esting. It is in these two localities, forming one 
island, that most of our alpine plants are found. 
The next highest hills are in Orphir and Rousay— 
the Ward of the former rises to 881 feet, and 
Blotchnie of the latter to 821 feet. 
When considering the altitude at which a par- 
ticular plant is likely to be found, latitude also has 
to be taken into account. For instance, I find that 
Thalictrum alprna grows in several places in Orkney 
within 100 feet above sea-level—near Hobbister, 
Stenness ; Scockness, Rousay ; and elsewhere. I have 
found Draba wncana at the Hammars of Syradale, 
Firth, not more than 400 feet above sea-level ; and 
again on Blotchnie, 800 feet high. Silene acawlis 
grows at the Hammars of Ward Hill, Hoy, 600 feet 
high ; and on Skea Hill, Westray, only 250 feet 
high. Then Carex rigida grows near the top of 
Ward Hill, Hoy; but I found one plant on Kirbuster 
Hill, Birsay, 335 feet high. If we compare these 
with the limiting altitudes given in Dr Whyte’s 
“Flora of Perthshire,’ we find that Thalictrum 
alpina has its lowest limit of 950 feet in Atholl. 
Draba wecana has a limit of 1000 feet in Atholl; 
and Silene acaulis has its lowest limit of 1200 feet 
in Breadalbane. The middle of Perth lies in latitude 
