Графични страници
PDF файл
ePub

Having considered the meaning of individual, species, genus and family, and of the characteristics by which these are grouped together, let us take a general view of this subject.

It is evident by the formation of species, genera and families, that every species should offer the essential characters of the family and genus to which it belongs; while the marks which distinguish this species from another species of its genus, will be such as do not belong to the whole genus or family. The different genera in families are also distinguished by characters which do not belong to the whole family ; every individual, then will possess its specific character, its generic character, and its family character.

The specific character is less important than the generic, as it is mostly founded on the characters of the organs

of vegetation, which we have seen are isolated and less important than the coexistent characters. We often find in the analysis of plants, a great difficulty in determining their species, from the want of more definite marks of distinction.

Generic characters are mostly of the coexistent kind, and are more valuable than the specific characters. The distinctions of genera are usually much more apparent than those of species ; as a rose can be more easily distinguished from a pink, than one species of rose from another species. Families are grouped together by marks of resemblance found in genera. These family characters are of all the most important.

In the artificial classes and orders we depend on what we have before termed factitious characters.

In species, genera and families, the essential characters are also natural characters.

LECTURE XXII.

Natural Families. We will now consider the vegetable kingdom as divided into natural families. We first find the general division, Acotyle. donous plants; these are the lowest in the scale of vegetable life, resembling, in many respects, the lower orders of animals; like them, simple and almost homogeneous in structure, and chiefly composed of cellular texture.

General view of the subject of classification-Which is the more important, the specific or generic character ?-Why are generic characters most valuable ? - How are families grouped together ?- Artificial classes and ordersFirst general division of plants.

Acotyledons.*

Class 1.
Embryo destitute of cotyledons, and a separate albumen.

These are the plants which are contained in the class Cryptogamia of the artificial system.

Fungi, or mushrooms; these are either parasitical, or spring from the ground naked or enclosed in a volva. The substance of mushrooms is, in some species, like cork or leather ; in oth. ers, soft, fleshy and juicy. They are round or flat; some have a head called a pileus (signifying hat). They have neither leaves or flowers. Instead of anthers they have a scattered, external or internal powder. Instead of pistils they have or. gans, which resemble thin plates, wrinkles, pores, tubes, &c. In these organs, exists a substance analogous to seeds, which germinates and reproduces the species. The different species of fungi are known by the common names of toad-stool, puffball, &c.

Mosses, instead of anthers, have collections of tubes which evolve a substance analogous to pollen. The pistillate flowers are collections of many in one group; their germ, instead of a corolla, is covered with a membrane called a calyptra (veil), whose summit admits the pollen. The fruit is a capsule, opening by a lid, having a margin either naked or fringed, with a certain number of teeth either in a single or double row. The seeds of mosses are very minute. The mosses are herbaceous, leafy and mostly branched; their roots are fibrous ; some are annual, others perennial.

Ferns exhibit no other fructification than capsules which grow on the back or edges of leaves. The leaves are called fronds; the stems are called stipes. Lichens, sea-weeds, &c. which belong to this class, will be considered under the artifi. cial class, Cryptogamia.

The second grand division of the vegetable kindom contains the 2d, 3d, and 4th classes of Jussieu's method.

Monocotyledons.

CLASS 2. Stamens hypogynous (below the germ). Embryo with one cotyledon. The characters of this class are ; stamens inferior, calyx inferior when present ; stamens seldom indefinite ; leaves mostly alternate and sheathing.

* See Jussieu's classes, page 169.

Characters of class 1st_Fungi_Mosses Ferns-Second grand division Characters of class 2d.

This class contains more than twenty families. Aroides constitute a family, of which the genus arum (wild turnip) is an important member, and from which the name is derived ; oides, is derived from the Greek, and signifies resemblance; thus aroides denotes plants resembling arum. This family have that kind of inflorescence called a spadix, surrounded by that form of calyx called a spatha. Their leaves are sheathing, alternate, and radical.

Gramina, or grasses, constitute an important family; they have generally three stamens and one germ. The embryo is small and attached to a farinaceous albumen. In germinating, the cotyledon remains attached to the albumen and nourishes the plume.* The roots are fibrous, and capillary. The culms are cylindrical; and either hollow, or pithy. The flower and calyx are scales, called glumes. The chaffy flower, single seed, mealy albumen, situation of the embryo, and method of germination distinguish, in a peculiar manner, this family.

Class 3. Stamens perigynous (around the germ). Fruit with three cells. Embryo small, with a large albumen.

Palms. In this class we find the family of the palms (Palma), which have a corolla deeply parted into 6 segments, the 3 outer ones being the smallest. The stamens and pistils are on separate plants; the number of stamens is usually 6; the filaments are often united at their base. The germ is su. perior, or above the calyx. The fruit is a berry or fibrous drupe, the albumen of which is at first tender and eatable, and at last becomes hard.

The stems of palms are usually undivided, lofty, and round : they are not composed of concentric circles, being endogenous, or growing internally; they are scaly from the remains of the indurated foot stalks of leaves; in treating of endogenous stems this peculiarity was observed. The leaves of palms appear in a terminal tuft, alternate and sheathing.

* See Fig. 90.

Aroides-Gramina--Characters of class 3d-Palms.

Fig. 96.

d

Fig. 96 repd d

resents a young palm tree (Chamærops humilis); at a is the fibrous root; b

C, represents the oldest part of the stipe, shewing by the

lines and dots the 6 b

place of insertion of the first leaves; cb, represents the upper part of the stipe, still covered with the sheathing bases of the peti. oles; d represents the crowning, terminal leaves these are petioled, fan-shaped, plait

ed when young ; b

the petioles are armed with prickles. Palms live to

a great age; they are the product of tropical regions, and afford valuable food.

Liliaceous plants (Liliaca), consist of six petals, spreading gradually from the base, and exhibiting a kind of bell-form appearance, but differing from the bell-form flowers in being polypetalous. The number of stamens in these plants is generally 6, sometimes but 3; they are usually alternate with the petals. The germ of the liliaceous plants is always of a triangular form, and contains 3 cells; the roots are mostly bulbous. The lily has a scaly bulb; the tulip has a root, which seems almost solid and tuberous.

The calyx is mostly wanting in the liliaceous plants, the stems are simple, without branches, the leaves entire, and nerved. To this family belong the tulip, lily, crown-imperial, dog-tooth violet, &c. Plants of this natural family usually belong to the artificial class Hexandria ; the crocus, having three stamens, belongs to the class Triandria.

Asparagi. We find here, closely connected with the Lilia

a

a

Describe Fig. 96—Liliaceous plants-Asparagi.

ceous plants, some other families, among which is the asparagi, from asparagus, one of its most important genera.

The family asparagi, is distinguished by monopetalous corollas, divided in. to 6 segments. The fruit is mostly pulpy and contains 3 cells. This family contains the genus Convallaria (lily of the valley), Trillium, fc.

Narcissi. The family Narcissi contains the genus Narcis. sus, Amaryllis, Hypoxis, Pontederia, fc. Their 6 stamens are inserted into the tube of the corolla. Their roots are mostly bulbous.

Irides. This family is so named from Iris, one of the most important genera.

The leaves in this family are alternate, sheathing, and sword-shaped (ensiform). The flowers are often attended by sheaths of two valves. We find here the Ixia and Sysirinchium.

CLASS 4. Stamens epigynous (above the germ). ORCHIS PLANTS (Or. chides). This family is distinguished by having, in place of stamens, glutinous masses of pollen, sometimes sessile, and sometimes supported by short filaments. The root has usually two knobs. * In this family are the Orchis genus, from which it takes its name ;- the genus Cypripedium, or lady's slipper, which takes its name from its large nectary resembling a shoe; the Cymbidium, or blue eyed grass, &c.

Dicotyledons. The third general division of the vegetable tribes includes the last eleven classes of Jussieu's method.

Class 5.
Apetalous ; stamens epigynous, (above the germ). The
characters of this class are a calyx superior, and of one leaf;
corolla wanting. It contains but one family, Aristolochiæ.

CLASS 6.
Apetalous; stamens perigynous (around the germ).

We have in this class, the family PROTEÆ ; these flowers, being variable in their characteristics, received their name from Proteus, a fabulous deity, remarkable for his transformations. We find here the family Lauri, which contains the genus Laurus. The family Polygoneæ is chiefly important as con. taining the genus Polygonum; the name of this genus is deri

* See Fig. 90, C.

Narcissi-Irides-Characteristics of Class 4th-Families most distinguished in this class-- Third general division--Characters of class 5th, &c. Of class 6th, &c.

4

« ПредишнаНапред »