RARE PLANTS IN BRITAIN. 
S 7 
collected it there when a youth) ? I might point you to Asarum 
europaum in two or three neighbouring stations in South Salop ; 
to the Lcucoium vernum, apparently a denizen near Charmouth, 
and Lcucoium cestivum, which 1 have myself gathered in that 
unpromising botanical hunting-ground, Plumstead Marshes ; 
to Astragalus alpinus, which I searched for in vain on little 
Craigindal in Braemar ; but of which I have abundant speci- 
mens sent me by a commiserating game-keeper to assure me 
that there it is, well established ; to Lastvea rigida, which I have 
gathered in abundance on that one zone of mountain limestone 
that it affects, and Lastvea cristata, which confines itself to a few 
English bogs, and is now nearly extirpated by the dealers’ 
shameless greed. 
I have not so much as touched the question of aliens and 
casuals — how they came, and why they have succeeded in 
becoming virtually denizen, such as Pcconia corallina on Steep 
Holme Island ; Crocus vermis , which empurples the pastures 
•every spring between Nottingham Castle and the Trent, and 
which is succeeded in autumn by the rarer C. nudiflorus. L ilium 
Martagon , which I have seen in abundance in a copse near 
Mickleham in Surrey, is a puzzle ; it has been known there for 
between 200 and 300 years. I met with a similar puzzle, not 
recorded in the botanical books, many years ago in South Wales, 
viz., a large patch of Lilium pyrenaicum growing by the roadside 
about midway between Haverfordwest and St. Davids — far from 
any village or cottage, but doubtless an escape from cultivation 
introduced somehow. Many other such examples are doubtless 
within the experience of my readers. 
And now we come to that question which I avowed myself 
•in the outset unprepared to answer, or even to propound a 
theory in aid or lieu of response. Every possible suggestion as 
to their capricious distribution is beset with difficulties. 
The explanations suggested broadly are : — 
(1) Continuity of land in earlier geological time. — According to 
this hypothesis they are survivals, which have defied the vicissi- 
tudes of changed climate and circumstances. But this fails 
entirely to account for the “ Botanic gardens,” and for the bare- 
ness (botanically speaking) of miles of equally suitable nurseries. 
When applied to individual cases it fails to satisfy. 
(2) Winds. — The least satisfactory of all the proposed factors 
in the problem. It might account for the dissemination of the 
minute spores of ferns, but hardly of the rank and file of flower- 
ing plants. The wind theory proves at once too much and too 
little. 
(3) Sea Currents. — This will account for some of our pheno- 
mena, e.g., the presence of Adiantum Capillus-V eneris along the 
south-west and western shores of Britain and Ireland ; the dis- 
tribution of Asplenium lanceolatum, and Lastvea amnia right up into 
Ross-shire (where I have seen it), for the presence of Erica 
mediterranea (modified into the form hibernica) in the far west of 
