132 THE ESSEX NATURALIST
shelter belts in the exposed fells and dales and also being a
conspicuous woodland denizen, while- it is a common seaside
and town tree, standing up to the harsh sea winds of the former
locality as well as to the smoke-laden atmosphere of the latter.
The Walnut is found chiefly in the open in this country but
occasionally it is met with in woodlands, as for example, a fine
specimen at High Beach, well within the Forest but possibly on
the site of an old cottage garden. Like its old-world relative,
the beautiful American Black Walnut (Juglans nigra L.) is also
sometimes grown in Britain, but not for the sake of its nuts,
which have been described as "edible but not palatable."
Of other broad-leaved trees, even our Common Elm (Ulmus
procera Salisbury) is claimed by some to be an introduction,
although since it is unknown as an indigenous tree outside
Britain we are, perhaps, justified in regarding it as one of the
trees which the Romans did not introduce. As native trees we
can lay certain claim to but one poplar—the Aspen (Populus
tremula L.); possibly, however, the Grey Poplar (P. canescens
Smith) is a native of the southern and eastern parts of Britain,
while the Black Poplar (P. nigra L.) may also be indigenous,
although in spite of its wide distribution in Europe it is generally
regarded as an alien which has become naturalised. The White
Poplar (P. alba L.) is a native of south-eastern Europe and parts
of western Asia and is not common in Britain, where it is fre-
quently confused with the Grey Poplar. The Lombardy Poplar
(P. italica Moench.), so familiar a tree of our landscape, is not
indigenous, although its native country is unknown ; it was intro-
duced about a couple of hundred years ago and most of the trees
here are males, for the female tree has a less closely fastigiate habit
and is less favoured. Our commonest Poplar, the Black Italian
Poplar (P. serotina Hartig.) is a hybrid, with the Black Poplar and
a North American Cottonwood (P. deltoidea March), for its
parents; it is widely planted as it produces clean timber at a fast
rate. This by no means exhausts the poplars of our countryside;
trees of this genus seem to have assumed popularity as roadside
trees and one cannot go far along the arterial roads without en-
countering one or more species. One has even been used as a road
sign by the Ministry of Transport, which has selected Lombardy
Poplar for planting at cross-roads as a warning to motorists.
Evidently it is considered that botanical education in Britain
has advanced sufficiently for the motorist to be able to dis-
tinguish the form of this tree, even if he does not know its name.
Of the numerous oaks, two species may be selected for
mention here. The Holm Oak (Quercus Ilex L.) with its ever-
green habit and magnificent crown, is a native of the Mediter-
ranean region but has been grown in Britain since the 16th