900 
Wilson.—Plant Distribution in the 
Origanum vulgar e, L. 
Clinopodium Acinos, 0. Kuntze. 
Clinopodium vulgare, L. 
Clinopodium Calamintha, O. Kuntze. 
Thymus Serpyllum , L. 
Mercurialis perennis , L. 
Quercus pedunculata, Ehrh. 
Ophrys muscifera, Huds. 
Orchis pyramidalis , L. 
Habenaria bifolia , R.Br. 
Taxus baccata, L. 
Anomodon viticulosus, H.T. 
Neckera complanata , Hueb. 
(£) Plants found on the Tertiary deposits but absent from or only 
occasionally on the Chalk and Clay with Flints :— 
Hypericum pulchrum , L. 
Oxalis Ace to sella, L. 
Potentilla silvestris , Neck. 
Oenothera biennis, L. 
Circaea lutetiana, L. 
Aspenda odor at a, L. 
Hieracium umbellatum, var. 
coronopifolium, Bernh. 
Campanula Trachelium, L. 
Calluna Erica, DC. 
Stachys Betonica , Benth. 
Lysimachia nemorum, L. 
Lysimachia Nummularia, L. 
Rumex Acetosella , L. 
Quercus sessiliflora, Salisb. 
Neottia Nidus-avis, Rich. 
Juncoides pilosum, O. Kuntze. 
J unco ides sylvaticum, O. Kuntze. 
praecox, L. 
Jlexuosa, L. 
caespitosa, L. 
Festuca ovina, L. 
Orthopyxis androgyna (L.), P. Beauv. Georgia pellucida , Raben. 
Leucobryum glaucum, Schp. Diplophyllum albicans, L. 
A general consideration leads to the conclusion that plant distribution 
in the districts investigated is greatly influenced by the composition of the 
soil. This, however, is not by any means the only factor involved. Whether 
a species shall or shall not exist in a certain situation depends on the whole 
of the conditions obtaining in that place. Some of these, such as soil com¬ 
position, altitude, water supply, and light intensity, evidently have a pre¬ 
ponderating influence, but, in addition, many others are no doubt present, of 
which the existence is unsuspected. The variation of any one condition 
may determine the presence or absence if all the other conditions remain 
constant. 
Since this is the case it is necessary to emphasize the circumstance 
that the present investigation has been confined to a comparatively small 
district. It is not desired to make any general statements as to the distri¬ 
bution of species outside this area. It will be apparent to those familiar 
with other types of vegetation that many of the peculiarities of distribution 
here described do not hold good for other localities. The absence of a plant 
from a particular formation in the district investigated does not necessarily 
imply that the species is absent in other districts and under other conditions. 
