184 
PROCEEDINGS OE SOCIETIES. 
languished out an existence,—this supposition being strengthened by 
the fact, that the Irish localities recorded for it are adjacent to, or at 
least in the same districts as those in which Polystichum Lonchitis, an 
undoubted boreal species, is found (the late Professor Smith, in his de¬ 
scription of the Plora of the Alps, vide “ Natural History Review/’ 
page 48, vol. iv., mentions his having remarked these ferns growing 
abundantly in juxtaposition at a considerable elevation). 
Of the place of origin of Trichomanes radicans and Asplenium acutum 
there can be little doubt, Lusitanian is stamped on every fact con¬ 
nected with their distribution. 
This view of the origin of Trichomanes radicans enables us to re¬ 
concile the seeming contradiction of its present and past distribution in 
the British Isles; for, looking at L . Fcenesecii as a member of the same 
Plora, that this is so is evident, since the district in which it is at 
present most characteristic and abundant also furnishes such confessedly 
Lusitanian types as Erica cilia/ris, E. Sibaldis, E. Mediterranean Asple- 
nium acutum, A. lanceolatum, Simethis bicolor, Pinguicula grandiflora, 
&c., among plants; and among animals, Pufo calamita, Helix pisana, 
Anthrocera minos {?), Geomalacus maculosus , Echinus lividus, Cossonus 
Tardii, Thia polita, &c.,—forms sufficiently characteristic to mark the 
district as possessing a great Lusitanian colony, many of the species not 
occurring elsewhere in Ireland and in England, only in the southern 
counties. 
Giving due weight to the difference of habit of growth,—Tricho¬ 
manes requiring three to four years for the full development of its 
fructification, and Loph. Fcenesecii perfecting its spores in the course of 
a season; bearing in mind the different physical conditions under which 
these two species are capable of existing,—an examination of their pre¬ 
sent distribution furnishes at once the clue as to how Trichomanes could 
have ever occurred atBellbank (Yorkshire), and Powerscourt (Wicklow). 
The following general laws of distribution explain the whole diffi¬ 
culty :— 
I. A species having spread from its centre, that disturbing causes in¬ 
compatible with its existence may arise at any point in the track 
of that distribution; the range of its existence may cease at this 
point, and the continuity of the distribution be destroyed, giving 
rise to a colony or colonies. 
II. That this interruption of continuity may proceed even to the total 
destruction of the capital centre, the colony or colonies remaining 
in vigour, or at least existing subsequent to the destruction of the 
capital. 
III. That the disturbing causes having been removed, and the range 
of existence being thus restored, the species may spread from this 
colonial centre or centres as from the capital, or even re-colonize 
the capital. 
Let us examine in this point of view the recorded range of Trichi. 
radicans and Loph. Fcenesecii. Trichomanes fl ourishes in a district extend¬ 
ing from about 51° 30' 1ST. to 52° 40' JNT. (Bantry being the most southern 
