NOTES ON ALIEN AND CASUAL PLANTS. 213
In this neighbourhood a building estate is generally a piece
of land on which one or more roadways are marked out, kerbed,
ballasted with coarse shingle and then left to Nature's tender
mercies, a house or two being often put up here and there just
to show what is intended ! The coarse shingle gradually gets
covered with a variety of plants, of which the common buttercups,
clovers, dandelions, plantains, hawkweeds, docks, goosefoots,
grasses, shepherd's purse, groundsel, and knot-grass furnish
by far the greater part, the seeds being, no doubt, mostly
supplied from local stock, but a fair proportion probably come
with the shingle, and amongst these are sometimes those of
aliens or casuals, which may not appear until a year or two
after their arrival, when some chance disturbance of the stones
gives them an opportunity to germinate. I should like to say
here that I wish to claim your indulgence for an incidental
reference now and then to interesting points in connection with
plants which are not aliens or casuals, and therefore, strictly
speaking, should not be mentioned at all.
On building sites in Hale End, I have met with Viper's
Bugloss (Echium vulgare), Small-flowered Willow Herb (Epilobium
parviflorum), (Lepidium ruderale) Narrow-leaved Pepperwort, all
casuals ; also the denizen, Common Melilot (Melilotus
officinalis), and the colonist, Treacle-mustard (Erysimum
cheiranthoides) ; the last named only a few inches in height
when growing on the stony roadway, but reaching to its normal
height of about two feet on another estate where it grew on the
clay. According to Babington, this species is wild in the fens. I
have also found the Rosebay (Epilobium angustifolium) and Great
Willow Herb (E. hirsutum) in similar situations not exceeding
18 inches in height, but both occur of the normal stature of 4ft.
or 5 ft. in suitable spots elsewhere in the district. These would
therefore be "casual" on the dry stony ground and "native"
in damp spots. The aliens, Salvia verticillata and Canadian
Fleabane (Erigeron canadensis) have also occurred ; the former,
being a perennial, persists from year to year, but seems gradually
dwindling.
A heap of builder's rubbish, mainly consisting of mortar
refuse, cement, dust, bricks, and slabs of concrete, gradually
became overgrown with grass and weeds, among which appeared
a patch of the alien, Lepidium draba, and one specimen each of