Page:TheTreesOfGreatBritainAndIreland vol04B.djvu/21

Evergreen trees belonging to the order Coniferæ; bark containing numerous resin- vesicles ; branches whorled. Buds, with numerous imbricated scales, with or without resin, usually two to five at the ends of the branchlets, the central bud terminal and largest, the others surrounding it in a circle on upright shoots, whilst on lateral branchlets those on the upper side are not developed ; buds also occur rarely and few in number in the axils of the leaves on the branchlets below. Branchlets of one kind, usually smooth, but in certain species grooved, with raised pulvini; each season’s shoot’ marked by a sheath at the base, composed of the persistent bud- scales of the previous spring.

Leaves on fertile and barren branchlets, often different in length and thickness and in the nature of the apex; arising from the branchlets in spiral order, radially disposed on vertical shoots, but variously arranged according to the species on lateral branchlets; persisting for many years and giving the tree a dense mass of foliage; leaving as they fall circular scars on the branchlets; sessile, but usually narrowed just above the expanded circular base ; linear, flattened and thin in most species, quadrangular in section in a few species; ventral surface always with two greyish or white stomatic bands, one on each side of the raised green midrib; dorsal surface with or without stomata, which when present are either in continuous lines, as in the quadrangular-leaved species, or are confined to near the tip of the leaf in the middle line, as in some flat-leaved species; apex acute, acuminate, or obtuse, notched or entire, spine-pointed in one or two species; resin-canals* two, constant in position for each species in the leaves on lateral branchlets, but in some species * differing in position in the leaves on the upright or fertile branchlets, either median,

1 In A. bracteata, all the bud-scales usually fall off, leaving ring-like scars at the base of the shoot.

2 The position of the resin-canals is easily seen on examining a thin section with a lens ; and can often be made out by squeezing the leaf, after it is cut across, when the resin will be observed exuding from the two canals.

3 In A. pectinata, A. cephalonica, and A. Nordmanniana, the resin-canals are marginal in the leaves of lateral branches, and are median in the leaves of cone-bearing branches. Cf. Guinier and Maire, in Bull. Soc. Bot. France, lv. 189 (1908).