XLV.— THE ALDER. 
Alnus rotundifolia Miller. 
T HE Alders, of which there are some fourteen species, belonging mostly to North 
Temperate regions, differ from the Birches in the persistence of their woody 
catkin-scales as a little cone-like structure after the fruits have fallen. Our one 
British representative of the genus, Alnus rotundifolia Miller, is confined to the 
Palasarctic Region. Its distinctive feature is its roundish leaves, with their wedge- 
shaped base, wavy and toothed margin, short stalk, obtuse apex, and five to seven pairs 
of lateral veins — which become a glossily dark olive-green on both surfaces. These 
leaves are tristichous, the shoots bearing them being slightly triangular, as also is the 
cross section of the pith, whilst the glutinous hairy surface of the leaves when young 
gave the tree the name A. glutinosa Gaertner, by which it has long been known. 
Another prominent character is the short stalk that supports the oval resting-buds 
which, with the young twigs, vary from a greenish-brown to a red-brown, with a 
pronounced violet hue and a whitish resinous bloom. 
Though it may reach a height of seventy feet and a girth of nine feet, it seldom 
exceeds half those dimensions. Gilpin in his “Forest Scenery” writes : — 
“ He who would see the Alder in perfection must follow the banks of the Mole in Surrey, through the sweet vales of 
Dorking and Mickleham, into the groves of Esher. The Mole, indeed, is far from being a beautiful river : it is a quiet and 
sluggish stream ; but what beauty it has it owes greatly to the Alder, which everywhere fringes its meadows, and in many 
places forms very pleasing scenes, especially in the vale between Box Hill and the high grounds of Norbury Park.” 
As its rich masses of young foliage overhang the golden beds of Marsh Marigolds, 
or, later in the year, it forms a background to foamy banks of Meadow-sweet, and 
the gorgeous magenta spikes of the Loosestrife, the Alder is certainly of value in 
the landscape ; but, as Sir Thomas Dick Lauder rightly says, when editing Gilpin’s 
work, the species is as often associated with the more rugged scenery of Scottish 
glens. Some of the most striking individual trees which I know are a few gnarled, 
crooked, and round-headed standards, of no very exceptional size, in a mountain 
glen among the ancient Scots Firs of the forest of Ballochbuie, near Balmoral. 
The Alder is more tolerant of stagnant water than any other European tree ; 
and this may be in part explained by its possession of numerous tubercles upon its 
roots, the work of a symbiotic Bacteroid by whose assistance the tree is enabled to 
utilise free atmospheric nitrogen. Like all water-side plants, it retains its leaves 
longer than the deciduous trees of dry situations, keeping them sometimes until 
January ; and, as they do not change colour in autumn, its winter verdure makes 
us appreciate it even more. 
The bark of the larger stems is nearly black and is full of clefts, as was noticed 
by Virgil in the passage which Dryden translates — 
“As Alders in the spring the boles extend, 
And heave so fiercely that their bark they rend.” 
