The absence of the ordinary bright green colours of vegetation is another peculiarity of this flora, almost all the plants having glaucous or whitened stems. Foliage is reduced to a minimum, the moisture of the plant being stored up in massive or fleshy stems against the long-continued drought.
As a picturesque tree, for park and ornamental plantation, it is among the best of the conifers, its colour and form contrasting yet harmonizing with the olive green and rounded outline of oaks and beeches, or with the red trunk and glaucous foliage of the pine.
The white spruce (Picea alba), sometimes met with in English plantations, is a tree of lighter growth than the black spruce, the branches being more widely apart; the foliage is of a light glaucous green; the small light-brown cones are more slender and tapering than in P. nigra, and the scales have even edges.
C. atlantica, the Atlas cedar, has shorter and denser leaves than C. Libani; the leaves are glaucous, sometimes of a silvery whiteness, and the cones smaller than in the other two forms; its wood also is hard, and more rapid in growth than is that of the ordinary cedar.
Correlated with their life in dry situations, the bulk of the tissue is succulent, forming a water-store, which is protected from loss by evaporation by a thickly cuticularized epidermis covered with a waxy secretion which gives a glaucous appearance to the plant.
The twigs are densely clothed with flat spreading linear leaves of a fine glossy green above and glaucous beneath; in the old trees they become shorter and more rigid and partly lose their distichous habit.
The leaves are glaucous and smooth like those of a swede turnip. For a seed-crop rape is sown in July or early August in order that the plants may be strong enough to pass the winter uninjured.
The leaves in a young state are not glaucous, but sap-green in colour and rough, being very similar to those of the turnip, to which the plant is closely related.
Lecanora metaboloides, Lecidea decolorans), while sometimes they are white or glaucous, rarely greenish, pruinose.
(Gentiana acaulis) and London pride (Saxifrage umbrosa),, Cerastium tomentosum, Stachys lavata and the beautiful evergreen Veronica rupestris with sheets of bright blue flowers, close to the ground, or by some of the finer grasses very carefully selected, such as the sheep's fescue (Festuca ovina) or its glaucous-leaved variety.
Boutignianum, pale rose, both have glaucous leaves tipped with purple; S.
Aquilegifolium, 2 ft., purplish from the conspicuous stamens, the leave's glaucous, is a good border plant; and T.
The Alternantheras, Amaranthuses, Iresines and Coleus Verschaffelti furnish high and warm colours; while Pyrethrum Parthenium aureum yields greenish-yellow; Thymus citriodorus aureus, yellowish; Mesembryanthemum cordifolium variegatum, creamy yellow; Centaureas and others, white; Lobelia Erinus, blue; and the succulent Echeverias and Sempervivums, glaucous rosettes, which last add much to the general effect.
The largest species of the group are the glaucous gull and greater black-backed gull, L.
In diameter at the base, and gnarled twisted boughs, densely clothed at the extremities with glaucous green foliage, which contrasts strongly with the fiery red-brown bark.
The Scotch fir is a very variable tree, and certain varieties have acquired a higher reputation for the qualities of their timber than others; among those most prized by foresters is the one called the Braemar pine, the remaining fragments of the great wood in the Braemar district being chiefly composed of this kind; it is mainly distinguished by its shorter and more glaucous leaves and ovoid cones with blunt recurved spines, and especially by the early horizontal growth of its ultimately drooping boughs; of all varieties this is the most picturesque.
The somewhat glaucous leaves form dense tufts at the ends of the branches, and are 4 or 5 in.
In diameter, and weighing more than 4 lb); the scales end in long hooked points curving upwards; the leaves are long, rigid, and glaucous in hue.
The leaves, short and glaucous, like those of the Scotch fir, have deciduous sheaths; the cones have recurved scale-points like those of the cheer pine.
Nearly approaching this is P. excelsa, the Bhotan pine, which differs chiefly in its longer cones and drooping glaucous foliage.
It is a straight-growing tree, with grey bark and whorls of horizontal branches giving a cylindro-conical outline; the leaves are short, rigid and glaucous; the cones, oblong and rather pointing upwards, grow only near the top of the tree, and ripen in the second autumn; the seeds are oily like those of P. Pinea, and are eaten both on the Alps and by the inhabitants of Siberia; a fine oil is expressed from them which is used both for food and in lamps, but, like that of the Italian pine, it soon turns rancid.
P. Ayacahuite, the common white pine of Mexico, spreads southwards on to the mountains of Guatemala, it is a large tree with glaucous foliage like P. Strobus, and yields a valuable resin.