CLVI.— DOG’S MERCURY. 
Mercurialis perennis Linne. 
W ITH no particular charm of individual form or of floral colour or perfume, 
the carpet of verdure which it affords at an early season in spring gives us a 
kindly feeling for the Dog’s Mercury, although we should never think of growing 
it in a garden or of gathering it for a bouquet. It often forms a marked feature in 
the landscape. Thus Dr. C. E. Moss, writing, in “ Types of British Vegetation,” 
on the Mountain Limestone of Derbyshire, says that it is much more abundant in 
woods on calcareous soils than on others : — 
“On soils, ’ he says, “which, during the summer months, may become temporarily very dry, sheets of dog’s mercury 
(Mercurialis perennis) often occur ; and this plant is in Derbyshire very frequently associated with the moschatel (Adoxa 
Moschatellina). At the beginning of April, in the Derbyshire dales, the dog’s mercury is about three inches high, its leaves are 
beginning to unfold, and a few stamens are ripe. At this time of the year, the moschatel is here flowering abundantly, and is 
almost hidden by the young shoots of the dog’s mercury. In the fairly dry portions of the ashwoods of the Peak district, this 
plant society of dog’s mercury and moschatel is a characteristic feature. The society is an excellent example of what Woodhead 
terms a ‘complementary’ society, as the roots of the dog’s mercury reach down to lower layers of soil than the roots of the 
moschatel, whilst the small and delicate shoots of the Adoxa receive their necessary shade from the larger and more vigorous 
shoots of Mercurialis. Before the end of June, Adoxa has entered on its long period of dormancy \ and the dull green leaves of 
the dog’s mercury, hiding its ripening berries, occur in extensive and monotonous stretches. It may, therefore, be said that the 
roots of the two species are edaphically complementary and the shoots seasonally complementary.” 
So too Messrs. Tansley and Rankin, writing in the same volume on the 
ground vegetation of the beech “ hangers ” on the sloping chalk hills of the 
southern counties, add : — 
“ in places where the foliage canopy is comparatively thin, Mercurialis perennis is the typical dominant, often covering the 
ground in continuous sheets, while Sanicula europcea , Viola R'vviniana , V, sylvestris , Fragaria vesca and Circaa lutetiana are 
generally abundant and locally dominant. Viola hirta , a pronounced calcicole, is also abundant and characteristic. The 
orchids Cephalanthera grandtfiora , and the rarer Helleborine violacea and H. atrorubens , are also characteristic, and Habenaria 
•virescens ( chloroleuca ) is frequent. Helleborus viridis , H. foetidus y Atropa Belladonna , Daphne Laureola y and Ruscus aculeatus are 
characteristic species of the more open spots in or on the outskirts of beechwoods.” 
The small genus Mercurialis belongs mainly to the xerophytic type of the 
Mediterranean region. It comprises seven species, all herbaceous, two of which, 
M . perennis Linne and M. annua Linne, occur in Britain. The latter, formerly known 
as French Mercury, is a doubtful native, occurring generally as a weed in gardens ; 
but, though it is necessarily dependent upon seed-production for its continued 
existence, since it is apparently capable of producing seed parthenogenetically, 
i.e. without fertilisation, it may well maintain itself. It has been employed as 
a boiled vegetable, the discovery of its wholesomeness being ascribed to the god 
Mercury, whence the genus derives its name. Compared to it, however, and to 
the so-called English Mercury (Chenopodium Bonus-Henricus Linn£), the poisonous 
Dog’s Mercury is, as the prefix Dog’s suggests, of no value. The Germans, in fact, 
sometimes call it Bose Heinrich (Wicked Henry) in contradistinction to the Chenopod 
Guter Heinrich. None of the genus has the milky latex of the Spurges, in which 
character they resemble the closely allied genus Ricinus , the Castor-oil plants. 
Being a perennial, the Dog’s Mercury is able to propagate itself largely by its 
slender, branching rhizomes, by means of which it becomes “social.” The branches 
