Special 2 ‘Mor pholegy 0 and Classifeiton. 375 
Orider > BETULACEA! (Fig. 480. ) ‘iveds or shrubs, with alter- 
nate simple leaves, and free deciduous stipules. Flowers moncecious, 
both male and female arranged in catkins, and subtended by scale-like 
bracts. Male flowers in threes in the axil of 
a bract, and formed of a two- or four-cleft perianth, 
in front of the teeth of which the stamens are placed ; 
female flowers also in twos or threes in the axil of 
a bract, but consisting simply of a free ovary with 
‘two loculi, in each of which is a pendulous ovule ; 
fruit usually a samara, and seeds exalbuminous. 
The two genera of this order, Getwla the birch, 
and Alnus the alder, furnish useful woods. From 
the bark of the birch is obtained the birch-oil used 
in the manufacture of Russia-leather, and impart- 
- ing to it its peculiar odour. 
Order 2. SALICACE. (Fig. 481). Trees or 
shrubs, with simple alternate leaves and deciduous 
stipules. Flowers dicecious, and both male and py. 480.—Bract of 
female always in catkins ; instead of perianth, each the birch, Betula, 
: oh oe with three samare 
kind has a few small scales or a glandular or cup- _in its axis, 
shaped fleshy disc. The male flowers consist, in 
addition, of from two to twenty-four free or monadelphous stamens; 
and the female of a free bicarpellary pistil, standing in the axil of 
a scale, and having generally two stigmas. The unilocular ovary con- 
tains a number of pendulous ovules attached to two parietal placente ; 
and the fruit is a two-valved capsule ; the seeds without endosperm, | 
but furnished: with a tuft of hairs. The two genera of which this order — 
is composed, Sa/’x the willow, and Populus the poplar, are divided 
into a large number of species, varieties, and hybrids, distributed over 
the whole globe. The nearer they approach the poles, the smaller are 
they in stature ; and the arctic willow, Sal¢x polaris, is only an inch in © 
height. Some species, as S, purpurea and ritbva, unfold their catkins 
before their leaves; among the best-known species are S. dabylonica 
the weeping willow, S. witellina the osier, S. a/éa the white willow, 
Populus tremula the aspen, P. nigra the black poplar, P. pyramidalis 
the Lombardy poplar, P. alba the white poplar, and P. dalsamifera 
the American balsam poplar. The wooed of some species is valuable 
on account of its toughness and elasticity, and is used for basket-work 
and other purposes. The bark of others, as S. pentendra and 
fragilis, is officinal, affording the substance known as salicine. 
* [The orders Betulacese ‘and Salicacer, together with Cupuliferse 
and Corylaceze from the cohort Quernales, constitute the Amentacese of 
the syllabus of the University of London.—ED. ] 
