Or impossible to fix upon characters so definite as to circumscribe completely any one group, while at the same time they exclude every member of the surrounding allied groups.

897. Second division. The Flowering plants are next resolved into two great provinces, indubitably marked by nature's own hand, and employed in every natural method. The following is their diagnosis.

Exogenae (εξω, without, yεvvuω, to generate), or Dicotyledonous Plants.

a, Growing by layers external to the wood, internal to the bark, b, Leaves net-veined, c, Flowers 4 or 5-parted, rarely 3-parted, d, Seeds with two or more cotyledons, and e, The radicle producing an axial root.

Endogenae, (εvδov, within, yεvvuω), or Monocotyledonous Plants.

898. Third division; - classes. The provinces are next broken into classes - groups of the third rank in extent. Two are constituted of the Exogens, viz.:

Angiospermae (ayyέoς, a vessel, σπέρa, seed) (oak, rose).

a, Flowers more generally perfect or complete, b, Pistils complete, inclosing the ovules, c, Seeds inclosed in a pericarp.

d, Embryo with only two cotyledons. Gymnospermae (yvvδς, naked, σπερa) (pine, yew).

a, Flowers imperfect and incomplete, b, Pistils scale-like, without a stigma, c, Seeds truly naked, that is, destitute of a pericarp d, Embryo mostly with several whorled cotyledons. Two classes are formed from the Endogens, viz.:

Petaliferae (πετaλov, petal, фέρω, to bear).

Plants of the endogenous structure, with flowers constructed on the usual plan; perianth of one or more whorls of petaloid organs, or wanting (lily, Orchis, rush). Glumiferae (gluma, husk, fero, to bear).

Plants of the endogenous structure, the flowers invested with an imbricated perianth of glumes, instead of petals and sepals (grasses, grains, sedges).

899. Divisions of the cryptogamia. This sub-kingdom is naturally divided into two provinces, the Acrogens, and Thallogens, - terms founded upon their mode of vegetation. The former include those tribes which make some approximation towards the Phaenogamia, the latter include the lowest tribes in the vegetable kingdom.

ACROGENAE (aĸρov, the summit, yεvvaω).

Flowerless plants having a regular stem or axis, which grows by the extension of the apex only, without increasing at all in diameter, generally with leaves, and composed of cellular tissue and scalariform ducts (Ferns, mosses, club-mosses, horsetails, etc.) Thallogknae (θaλλoς, green branch, yεvvaω).

Flowerless plants producing in vegetation a thallus, with no distinction of stem and leaf, or root, and composed of cellular tissue only (Lichens, fungi, etc.)

900. Classes of the flowerless plants. For the sake of analogy and an advantageous comparison with the Phaenogams, we may also regard these two provinces of the Cryptogams in the light of Classes founded upon their different modes of fruitbearing. Thus the Acrogens constitute the class

Angiosporae (ayyεioς, σπooa).

Acrogenous plants, producing their spores in sporangia (vessels) which burst when the spores are mature. GYMNOSPORAE (σπoρa).

Thallogenous plants reproduced by spores, which are produced in parent cells, either forming a part of the vegetating thallus, or growing upon the surface of some definite region of the thallus.

901. Fourth division - cohorts. The six classes, as above constituted, are still each of great extent, - too great for the comprehension of the learner, or practical use. A further division is therefore necessary. To effect this on strictly natural principles botanists have labored hitherto in vain. The truth is, the members of these several classes are united by affinities so equable as to render it impossible to subdivide, except by distinctions more or less arbitrary. So adjacent territories, where rivers or other natural boundaries are wanting, must bo separated by artificial lines.

902. The angiosperms are divided by De Candolle, in his great descriptive work "Prodromus Systematis Naturalis Regni Vegetabilis" into four sub-classes founded upon the conditions of the floral envelops, viz.:

1. Thalamifloroe, petals distinct, and (with the stamens) hypogynous.

2. Calycifloroe, petals (with the stamens) perigynous.

3. Corollifloroe, petals united, hypogynous, stamens epipetalous.

4. Monochlamydeoe, petals wanting.

903. The plan of Endlicher in his "Genera Plantarum" is more simple and convenient, and has been followed by American writers generally. He separates the Angiospermae into three "cohorts," thus:

1. Dialypetaloe (δaλvω, to dissolve). Exogenous plants, having both calyx and corolla, the latter composed of distinct petals (polypetalous), sometimes slightly cohering by the base of the stamens, rarely abortive.

2. Gamopetaloe (yaoς, union). Exogenous plants, having both calyx and corolla, the latter composed of petals more or less united.

3. Apetaoloe (a, privative). Exogenous plants with flowers having a calyx only, or neither calyx nor corolla (achlamydeous).

904. The class petaliferae may be conveniently separated into two cohorts, as follows.

1. Spadicifhroe. Endogenous plants with flowers having no perianth, or a scaly one, and borne on a thickened spadix, which is often enveloped in a spathe.

2. Ftorideoe. Endogenous plants with the flowers usually perfect and complete, the perianth double, 3-parted, the outer often and sometimes both green.

905. The class glumiferae is equivalent to the cohort Grami-noideae, including the sedges, grains, and grasses - a truly natural assemblage.

906. The class angiosporae consists of three cohorts defined as follows.

1. Sporogamia. Angiosporous plants, producing spores in which, when germinating, antheridial cells and archegonal, or ovulary bodies, are formed (Lycopodiaceae, Isoetaceae, Marsileaceae).

2. Thalbgamia. Angiosporous plants producing spores of one kind in spor-anges on the surface of the leaf or stem, the spore germinating into a green prothallus (629) on which are developed antheridia and archegonia, the latter giving origin to a leafy embryo (Equisetaceae, Filices).

3. Axogamia. Angiosporous plants producing antheridia and archegonia in the axils of the leaves or in buds, the fertilized archegonia giving birth to sporanges filled with spores, all reproducing the plant (Mosses, Hepaticae, Characeae).

907. The class gymnosporae consists of three cohorts, viz.:

1. Aerophyta. Thallogens growing and fructifying in the air, reproduced by spores formed in asci, and by green gonidia formed in the medullary layer of the thallus (Lichens).

2. Hysterophyta. Thallogens growing in or on decaying organic substances and fructifying in the open air, destitute of chlorophylle and starch, reproduced by spores formed in asci, by archegonal spores and by gonidea (Fungi).

3. Hydrophyta. Thallogens with a branching or foliaceous thallus; membranous, gelatinous, or cartilaginous in texture, containing either chlorophylle or a red coloring matter and often starch grains; growing in water, salt or fresh, or in moist substances in damp air (Algae).

908. The following synoptical arrangement of the above divisions and subdivisions will exhibit at a glance the relative position and mutual relations of each,