the Pinacew and Cicadeacee this order differs in the greater perfection of its reproductive organs, while the ovules are covered with a pericarpal integument, opening at the summit.” n the osperms, which connect the lower with higher forms of organisation, the transition is very distinctly marked. In Cycads the stem is simple and cylindrical, the departure from its terminal mode of development being exceptional and accidental, while the Conifers exhibit a constant tendency to a rapid evolution of leaf-buds in every axil. An increasing value in their products is also observable. The Cycads, for instance, yield a mucilaginous juice, mixed with starch, from which common articles of food are prepared. At the Cape of Good Hope the fruit of the various species of Encephalartos are called “ Catire bread,” and a kind of arrowroot is prepared in Mexico from the seeds of Dion edule. In Japan a sago is procured from the cellular substance occupying the stem of Cycas revoluta, and also from Cycas cireinalis in the Moluccas. Other species are also Ce utilised in the countries of which they are natives. The Pines and Fir-trees are chiefly valuable for their timber, and the Yews and their allies are valuable for their resinous products, and also for timber, which is unsurpassed for elasticity and durability;and in Amboyna the seeds of Gnetum Gnemon are eaten F. boiled, or fried, and the green leaves are a favourite vegetable eaten and cooked as spinach.

Crass VII.—ExoceEns.

The Dicotyledons of Jussieu, and the Exogens of more recent 2 botanists, include the more highly organised plants, which for “ while a cenMoreover endowed with proportionate vitality, tury or two terminates the existence of most endogenous ere some existing Exogens were monarchs of the forests at the be: & ginning of the Christian era.” As already eX] Jained, air add their new wood to the outside between the bark and wood ne last year’s growth.; Peal The class of Exogens numbers over 66,000. Their germinate! is exerhizal, the embryo with two or more cotyledonous 1*°" having a network of veins; the trunk formed of woody bundles

fibre, composed of dotted woody tubes alone; arranged round a central pith, forming either in eccentric rings, or in a homogeneous mass, but always having medullary plates radiating from the centre to the circumference, which are reproduced on the circumference of the trunk. Genera, 6,191; species, 66,225.

All botanists are agreed that the organs of reproduction may be expected to furnish the best characters for classification after those necessary for nutrition. Linnzus was of this opinion, and he made them to a considerable extent the basis of his system, but he mainly relied upon their number. The importance of the stamens and pistil did not escape the observation of Jussieu, who separated from all other Exoczns those having the stamens in one flower and the pistil in another, and he called them Dicurnovs. By this means he brought together a collection of natural orders corresponding with the monecious and diccious plants of Linnaeus. But, in carrying out his system, he excluded a vast number of truly diclinous plants. Some of these anomalies have been corrected by recent observers, and Dr. Lindley has divided the whole of the vast class of Exogens into (1) Dicirnous, (2) Hyroernovs, (3) Pertexnous, and (4) Epieynous Exocens.

Sup-Ciass I.—Diciinovus EXOGENS.:

HAVING MALE anp FEMALE, WITHOUT ANY TENDENCY TO BISEXUAL FLOWERS.

—. flowers mane =. without or with only one floral —— ' ‘uperior, embryo small, littleor no albumen; ovary one-celled, aarinacese oak of pies or two ascending, radicle ascendin g. This includes the She- on:

‘ eee Fs Ovary one-celled, ovules one, pendulous, radicle superior, including. the Maples, the Alder, Birch, plane trees, &c. }LXXVIIL. Betulncee. -yielain® (W0-celled, with numerous winged seeds, including the Balsam: Liaend tree€s with many-seeded capsules, and the several species of } LXXIX. Attingiacem. - tan. ry one-celled, with humerous cottony seeds growing at the base of a: } LXXX. Salicacer. “alved capsule, as in Willows and ow Hho — fragran| lled, with a single erect seed and superior radicle. The tuales of America, the Cape, and India are aromatic shrubs or | yxyxy, Myricacee.

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e 8nd flowers elled, with @ single ascending ovule, an inferior radicle, BOWS extensinenes bisexual. The beautiful and fragrant Oleastro ¢LXXXII. Oleagnaces. — ae ely over the Northern Hemisphere, down to the Equator. _

The AMENTALEs are declinous Exogens with unisexual flowers, __. Mmentaceous inflorescence, and incomplete calyx. These cha- : ee form an obvious bond of union in this important natural — og P; and a brief description of the Berutacz, or Birches, and 'CACE®, or Willows, are the most familiar examples we can

offer. They are trees or shrubs, with simple alternate leaves nearly orbicular in shape, with primary veins running nearly straight from the midrib to the margin; stamens usually distinct; ovary superior and two-celled; fruit membranous, indehiscent and one-celled; seed pendulous. The Birch-tree, Betula alba, is monecious, with alternate leaves, ovate and peteolate, accuminate and dentate or doubly dentate, green and glossy above, of a pale glabrous green below. Their straight upright stems, smooth silvery bark, long, round, slender, flexible, and pendulous branches, © render the Birch a graceful ornament in the landscape. The Birch is in flower in the month of April, when the white silvery bark produées the happiest effects contrasted with the deeper and more sombre tints which the trunk of the Elms and Oaks present. y The Alder, Alnus glutinosa, has stalked simple stipulate leaves. F lowers in male and female catkins, the male flowerets loose at: cylindrical, usually in threes on the pedicle of the scale; stamens,

Bract bearing two Ripe Catkin. Bract bearing three flowers female flowers. of the Alder.

Fig. 374. ie lene ale flowerets_ three or four inserted at the base of the divisions. Fem ee in dense ovate catkins, two together on roundish sessile fleshy ee with four smaller ones at their base, each with a small Ovary) ak two one-seeded cells. The glutinous leaves, red sap, and wi he fruit distinguish the only British species of Alnus from © Birches.: es of rivers, an areof#

Bract bearing two Ripe Catkin. female flowers. ract bearing two female flowers.

Plate VIII.—Alder Tree (Betula alba).

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monecious. In the month of February, after the leaves have appeared, the cylindrical elongated catkins composed of male flowers are left hanging, while the egg-shaped catkins composed of female flowers are erect and directed towards the sky. In the axils of each scale of the male catkin may be noted three flowers, one in the centre and two placed laterally; these three flowers are composed each of a perianthe of four divisions (Fig. 374), and of four stamens opposite to these divisions,- with bilocular anthers opening from without by two longitudinal slits. They are surrounded, independently of the scale of the catkin, by “pesecondary scales, two of which are to the right and two to the eft. In the axil of each scale of the female catkin, four secondary scales and two flowers may be observed; each of these flowers consist of a pistil only, the free ovary of which is surmounted by a short style divided into two stigmatic branches. The ovary presents two cells, in each of which is suspended an anatropal ovule. The fructiferous catkins are in the form of a Pine cone, with horizontal persistent scales, straightly juxtaposed and rendered coherent by a resinous substance spreading itself out ultimately to permit the fruit to escape. These fruits are compressed, surrounded on all sides by a coriaceous cork-like edging. They are unilocular, and enclose only one seed. |

The Sarrcacem, a small order of Amentales, consisting of the’ Willows and Poplars, are trees or shrubs with alternate simple leaves with deliquescent primary veins, frequently with glands on the edges, and deciduous or persistent stipules. Flowers amenta- Ceous, one-celled ovary, and numerous cottony seeds. These downy — Seedsof Willows and Poplars, growing at the base of a leathery two-valved capsule, cannot be mistaken. oS The Willows (Salix) are very numerous in species, varying in S Size from the dwarf (S. herbacea), with creeping underground _ ‘Stem and ascending branches, to S. Adba, the common Willow, thirty — - feet high; they consist of Willows, Sallows, and Osiers, generally = with round, slender, flexible branches, with simple entire stipu-_ a lateleaves, diccious inflorescence, and male and female flowerets _ f = long cylindrical catkins. The natural habitat of the Willow ‘Son the banks of sluggish rivers, and in low marshy places; the

Osier beds are generally found where they can be under water the greater part of the year; while the Sallows, as S. caprea, rather affect dry woods and hedges; others, as S. /anata, are. beautiful mountain shrubs, the fertile catkins of which are sometimes found a span long in Glen Dole and Glen Callater.

Willows abound in temperate regions, but decrease sensibly in number towards the South of Europe and in Algeria. They serve to consolidate the borders of water and rivers. The Willow furnishes means for the basket-maker’s work.

The White Willow (Fig. 375) is the most important of its species, on account of the large dimensions which it acquires: it is very productive in Osiers and Pollards.

The Weeping Willow (Salix Babylonica), of which we have already given a representation at page 66, is particularly remarkable for the length, flexibility, and graceful drooping habit of its branches,

n , {llow::

Fig. 375.— Male catkin of the Willow. Fig 376,—Female catkin of the Wi

which give it an appearance of melancholy grace. Its oon. ae unknown; we only possess the female specimen. ae cab

The Salix reticulata, Wrinkled Willow, isa very S™*" of from one to two feet high, which grows in the Alps, the ase — and on the Welsh and Scottish mountains. “ “a

The herbaceous Willow is also a very small shrub, with - herba- oe ing under ground and emitting branches almost completely ee

: ig : Fig. 375.— Male catkin of the Willow.

ite W Fillow (Salix alba).ate IX,—The Wh

ceous; it grows in the High Alps and the Pyrenees, in Mount Doré in Auvergne, and also in the Grampians. Willows are diccious; their flowers are in catkins, and solitary, with an axil to each scale of the catkin. They have no envelopes. Figs. 375 and 876

Fig. 377.—Male Flowers of Salix alba. Fig. 378.—Female Flower of Salix alba.

represent the male and female catkins of the Willow; 377 and 378 show the isolated flowers. »

The Poplars (Populus) are nearly allied to the Willows, and in the flowers they are only distinguished from them by the greater number of stamens, which are inserted on the internal face of a kind of cup.: The Black Poplar (Populus nigra) is among the larger of these trees, commonly known as the Swiss Poplar. The White Poplar (Populus alba), a fine tree with ample cyme, is furnished with ves remarkable for their extreme whiteness underneath, especially Upon the most elevated shoots. Fig. 879 represents this species. The Aspen (Populus tremula) is the only real forest-tree of this genus; it is of middle height, with leaves which are very mobile _ lM consequence of their length; they are compressed vertically, ___ Which leads to'the horizontal tremulous motion which distinguishes the tree and procured its name.; The Pyrammar Portar, originally from the Caucasus and Persia, was imported into Italy and France about the year 1749; it is remarkable for its erect branches which spring from nearly the base of the trunk, and altogether form a long, straight, pyramidal _. “yme: only the male plant of this species is known. | Among the Amentales the CasvARINEACES are for the most. ge

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