DUBLIN NATURAL HISTORY SOCIETY. 
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recorded station, and Cumailte Mountains, county of Limerick, its most 
northern), and as far east as about 7° 50' W., the Blaekwater valley re¬ 
presenting* the latter; the plant growing in greatest perfection, that 
is, fruiting most regularly and perfectly at Iveragh, and in the valley 
of the Blaekwater; the extreme humidity of the Killarney district, 
whilst encouraging the ordinary growth of the plant, interfering with its 
fruiting. 
Outside this well-marked district are two outlying stations, both, at 
the time of their discovery, sickly, and now extinct, or at least one of 
them: one, "Wicklow, situated in about 52° 10' IN’, and 6° 20' W.; the 
other, Bellbank, nearBingley, Yorkshire, about 53° 30' Y. and 1° 55' W. 
In all these districts Lophod. Fcenesecii is found luxuriant, but local 
in the latter two. 
Suppose these two plants to have made their entry into Ireland 
somewhere in that district which A sp leniurn lanceolatum, A. acutum , Adi- 
antum capillus Veneris mark out as the head-quarters of the Lusitanian 
Flora, and to have spread under favourable circumstances as far north as 
Yorkshire; that then, the two countries severed, the physical conditions 
of district were so altered as to destroy the balance necessary to the 
former’s existence in the intervening districts. This favoured spot at 
Bingley, where Bichardson gathered, one hundred and fifty years ago, 
the celebrated specimen which has so puzzled botanists, remained as the 
last haunt of Trichomanes radicans; whilst its hardier compatriot escaped 
the general destruction of Lusitanian forms so well as to supply us with 
abundant stations even much further north than this. Similarly the 
Wicklow station may be but an offset from that in the county of Water¬ 
ford, and may be even anterior to it, the chain of continuity being 
broken by some causes which caused the disappearance, plant by plant 
and station by station, of Trichomanes, so that the sickly plant discovered 
by Dr. Whitley Stokes and Miss Litton, in 1805, at Powerscourt 
Waterfall, at last alone remained to point out the old colonization of the 
district with the species. 
Some explanation of the set of terms already freely used is ne¬ 
cessary, viz., “ balance necessary to the plant’s existence.” By this is 
meant those degrees of intensity of physical agencies, especially light, 
heat, and moisture, compatible with the existence of any species, or, as 
we might otherwise express it, the physical range of its existence. The 
following series of laws express this more generally :— 
1. Every species requires light, heat, moisture, &c., for the due per¬ 
formance of its functions, and the quantity of these thus neces¬ 
sary may vary within certain fixed limits. 
2. That this limited standard may be still further either increased 
or diminished within certain further limits, without destruction 
of the life of the species, though usually at the expense of or 
deterioration of some of the functions. 
3. That the (1) standard of growth and (2) range of existence varies 
in species springing from the same centre. 
