152 
Brenchley . — The Weeds of Arable Land. III. 
Polygonum aviculare 
Ranunculus repens 
Rumex crispus 
Senebiera Coronopus 
Senecio vulgaris 
Sherardia arvensis 
Stellaria media 
Veronica Tournefortii 
\ 
- universally distributed. 
Sonchus arvensis — especially on clay. 
Chaerophyllum Anthriscus^ 
Fumaria officinalis 
Glechoma hederacea 
Silene inflata 
Veronica arvensis 
Viola tricolor t 
rare or absent from clay. 
Anagallis arvensis \ 
Myosotis arvensis L scarce on chalk. 
Poa annua ) 
Bartsia Odontites i 
Erysimum cheiranthoides 
Polygonum Convolvulus 
Scandix Pecten-veneris 
Taraxacum vulgare 
Triticum repens , 
absent from chalk. 
Some of the above species are both universally distributed and abundant 
in occurrence. Some plants (e. g. Polygonum aviculare, Chenopodium album , 
Viola tricolor , Cerastium vulgatum , Capsella Bursa-pastoris , &c.) show 
considerable morphological differences in different places, exhibiting varia- 
tions in habit, in the size and shape of the leaves, in the size and colour of 
the flowers. It is quite possible that ‘ splits ’ or varieties of these cosmo- 
politan species may ultimately prove to be as significant as species themselves, 
and that a certain split may be as definitely associated with a particular type 
of soil as homogeneous species of other genera. Massart 1 suggests that 
when a species is found colonizing very diverse habitats, some essential 
difference really exists between the plants, and that under the combined 
influences of variability and natural selection a species undergoes a trans- 
formation or ‘adaptation’ which is hereditary, in contradistinction to 
the ‘ accommodation ’ of an individual to place itself in accord with its 
habitat. 
1 Massart, I. : Le role de l’experimentation en geographic botanique. Rec. Inst. bot. Leo 
Errera, ix, 1912, pp. 68-80. Abst. in Bot. Centralbl., Band cxx, No. 14, pp. 353-4. 
