248
THE ESSEX NATURALIST.
Buttercup (Ranunculus acris L.). Occasional, and encouraged
by our gardener as an ornament, when vigorous plants
appear.
Creeping Buttercup (R. repens L.). Rather a dangerous weed
from its widely creeping runners.
Lesser Celandine (R. Ficaria L.). A troublesome weed in some
borders and difficult to extirpate on account of its bunches
of fleshy tubers. A tall form occurs in one border with
bulbils developed in the axil of every leaf ; this form is said
to have double the usual number of chromosomes in the
nuclei. The formation of bulbils is due to the action of a
parasite, according to recent observations.
Poppy (Papaver Rhoeas L.). A ; casual.
Opium Poppy (P. somniferum L.). A ; casual.
Fumitory (Fumaria officinalis L.). A ; casual.
Pale Fumitory (F. capreolata L. var. pallidiflora Jordan). One
plant only.
American Cress (Barbarea praecox Br.). A; a casual, often
grown for salads ; it is native to Europe and has been
introduced into North America.
Hedge Mustard (Sisymbrium officinale L.). On waste ground.
S. Columnae Jacq. This has appeared for four or five years on
one allotment; it is a native of South Europe, and seems to
be increasingly common in England.
S. pannonicum Jacq. A ; has appeared once ; the specific name
suggests that it is a native of Hungary.
Treacle Mustard (Erysimum cheiranthoides L. A ; not frequent.
Charlock (Brassica Sinapistrum Boiss.). A; frequent.
White Mustard (B. alba Boiss.). A ; not unfrequent.
Alyssum maritimum L. A; casual on waste ground.
Horse Radish (Cochlearia Armoracia L.). On waste ground; an
escape from cultivation ; its origin is unknown ; Hooker
suggests it may be the cultivated form of C, macrocarpa
W. and K., a native of Hungary.
Shepherd's Purse (Capsella Bursa-pastoris D.C.). Extremely
common, and very variable ; the rosette leaves are nearly
entire in some plants, in others they are deeply pinnatifid
with slender curved tips to the segments.
Wayside Cress (Lepidium ruderale L.). On waste ground.
Penny Cress (Thlaspi arvense L.). A ; not unfrequent.