BETULACE. 
SILVA OF NORTH AMERICA. 
49 
are fungal diseases very serious.! Several species are largely used in the northern United States and 
in Europe for the decoration of parks. Birch-trees can be easily raised from seeds,’ and their varieties 
can be propagated by grafting. 
Betula, the Latin name of the Birch, was adopted by Tournefort* and afterward by Linnzus for 
this genus. 
The fruit of Betula is sometimes infested in America by a minute 
Dipteron identical with or closely allied to a species of Cecidomyia 
which in the larval state lives within the nuts of Birches in Europe. 
1 Betula abounds in fungi, several of which are peculiar to it 
and easily recognized. The most striking and familiar species is 
Polyporus betulinus, Fries, very common at all seasons of the year 
on the white-barked Birches. It forms flattened hemispherical or 
dish-like masses of a corky substance ; at first these are nearly 
white but become brown with age, reaching sometimes a diame- 
ter of five or six inches and projecting at right angles to the 
trunks. The much larger, flatter, and harder fungus, Polyporus 
applanatus, Fries, from which ornamental brackets and so-called 
vegetable cameos are made, is also very common on the white- 
barked Birches, although it is also found on other trees. A number 
of the smaller species of Ascomycetes growing on Betula as Hy- 
poxylon transversum, Saccardo, Hypoxylon multiforme, Fries, Cenan- 
gium seriatum, Fries, have the peculiarity of bursting through the 
bark in transverse lines similar to the elongated lenticels which 
form the familiar streaks in the bark of the Birch. Diatrype disci- 
formis, Fries, dots the surface of the bark with numerous round 
black disks. 
to the genera Hypoxylon, Massaria, and Melanconis, which are 
Other Pyrenomycetes common on the Birches belong 
especially inclined to infest trees of this genus. 
The leaves of Birches are attacked by Melampsora betulina, Tu- 
lasne, one of the rusts, and in early summer the leaves of Betula 
populifolia are not infrequently injured by Exoascus flavus, Farlow, 
which causes yellow discolorations. Later in the season the leaves 
are found to be covered with small black bodies, the perithecia of 
pycnidial forms belonging to a number of different Pyrenomycetes. 
2 Cobbett, Woodlands, 155. 
3 Inst. 588, t. 360. 
CONSPECTUS OF THE NORTH AMERICAN SPECIES. 
EvUBETULA. 
Strobiles oblong-ovoid, sessile or nearly so, erect ; wing of the fruit not broader than the seed ; 
bark brown or yellow-gray, and, like the young branches, aromatic. 
Strobiles sessile, their scales glabrous; leaves ovate or oblong-ovate, heart-shaped or 
rounded at the base ; bark dark brown, sweet-aromatic 
Strobiles sessile or short-stalked, their scales pubescent; leaves ovate or oblong-ovate, 
1. BETULA LENTA. 
cuneate or slightly heart-shaped at the base; bark yellow or silvery gray, slightly 
aromatic. . . . . ... 
oe eh whl ehUle™hCUe™C™e”™C~«™s:C”:C«@@iSCC@&BEEDULLAAs LUT. 
Strobiles cylindrical, on slender peduncles erect or hanging, the wing of the fruit broader than 
the seed. 
Strobiles short or elongated; bark of young trunks and of the branches white on the 
outer surface, bright orange-color on the inner, and separable into thin sheets; young 
leaves and branchlets glandular. 
Strobiles slender, short, erect or spreading, on short peduncles, their scales pubes- 
cent; staminate aments solitary or rarely in pairs; leaves nearly triangular, 
long-pointed, usually truncate at the broad base, lustrous, on elongated slender 
petioles; bark chalky white, rather close. 
3. BETULA POPULIFOLIA. 
Strobiles stout, elongated and hanging on long peduncles, their scales glabrous; 
staminate aments clustered; leaves ovate, cuneate or rounded at the base, dull 
dark green; bark lamellate, creamy white and lustrous. . . . - - . = - 
4. BETULA PAPYRIFERA. 
Strobiles oblong, erect, their scales pubescent; leaves rhombic-ovate, acute at both ends, 
lustrous; bark of young stems and upper branches separating in thin persistent 
plates 
Strobiles short; bark close, dark brown, young leaves and branchlets glandular. 
5. BETULA NIGRA. 
Strobiles oblong, erect or hanging on long slender peduncles, their scales puberulous ; 
leaves thin and dull, broadly ovate, truncate or rounded at the base . - . + + + 
6. BETULA OCCIDENTALIS. 
