The Vegetable Kingdom is arranged in 5 Divisions.
Division I.--=Thallophyta=, =Stemless Plants=, or those which
are composed of a “thallus,” _i.e._ organs of nourishment which
are not differentiated into root (in the sense in which this term is
used among the higher plants), stem, or leaf. Vascular bundles are
wanting. Conjugation and fertilisation in various ways; among most of
the Fungi only vegetative multiplication.
In contradistinction to the Thallophytes all other plants are
called “Stem-plants” (“Cormophyta”), because their shoots are
leaf-bearing stems. The name Thallophyta (Stemless-plants) is
to some extent unsuitable, since many of the higher Algæ are
differentiated into stem and leaf.
The Thallophytes are again separated into 3 sub-divisions, namely:
Sub-Division =A.=--=Myxomycetes, Slime-Fungi=, with only 1 class.
Sub-Division =B.=--=Algæ=, with 10 classes:
Class 1. Syngeneticæ.
„ 2. Dinoflagellata, Peridinea.
„ 3. Diatomeæ, Diatoms.
„ 4. Schizophyta, Fission Algæ.
„ 5. Conjugatæ.
„ 6. Chlorophyceæ, Green Algæ.
„ 7. Characeæ, Stone-worts.
„ 8. Phæophyceæ, Brown Algæ.
„ 9. Dictyotales.
„ 10. Rhodophyceæ, Red Algæ.
Sub-Division =C.=--=Fungi=, with 3 classes:
Class 1. Phycomycetes.
„ 2. Mesomycetes.
„ 3. Mycomycetes, Higher Fungi.
Division II.--=Bryophyta or Muscineæ, Mosses.= These have
leaf-bearing shoots, but neither true roots nor vascular bundles. The
lowest Mosses have, however, a thallus. Fertilisation is accomplished
by means of self-motile, spirally coiled spermatozoids, through the
agency of water. From the fertilised oosphere a “fruit-body” (capsule)
with unicellular organs of reproduction (spores) is produced. The spore
on germination gives rise to the vegetative system, which bears the
organs of sexual reproduction; and this system is divided into two
stages--the protonema, and the leaf-bearing plant produced on it.
Alternation of generations:
I. The protonema and the entire nutritive system which
bears the organs of sexual reproduction.
II. The capsule-like sporangium, with spores.
2 Classes: 1. Hepaticæ, Liverworts.
2. Musci, Leafy Mosses.
Division III.--=Pteridophyta or Vascular Cryptogams=, =Fern-like
Plants= having leaf-bearing shoots, true roots, and vascular bundles
with tracheides and sieve-tubes. Fertilisation as in the Mosses. From
the fertilised oosphere the leaf-bearing shoot arises, which bears
on its leaves the reproductive organs, the spores, in capsule-like
sporangia. From the germination of the spore a small prothallium is
formed, which bears the sexual reproductive organs.
Alternation of generations:
I. Prothallium with organs of sexual reproduction.
II. Leaf-bearing shoot with capsule-like sporangia.
3 Classes: 1. Filicinæ, True Ferns.
2. Equisetinæ, Horsetails.
3. Lycopodinæ, Club-mosses.
Division IV.--=Gymnospermæ.= The vegetative organs are in the
main similar to those in the 3rd Division; special shoots are modified
into flowers for the service of reproduction. From the oosphere, which
is fertilised by means of the pollen-tube, the leaf-bearing plant is
derived; this passes the first period of its life as an embryo in
the seed, and continues its development when the germination of the
seed takes place. The organs corresponding to the spores of the two
preceding Divisions, are called respectively the pollen-grain and
embryo-sac. The pollen-grains are multicellular; i.e. they contain
an indistinct prothallium. In the embryo-sac a prothallium, rich in
reserve material (endosperm), with female organs of reproduction, is
developed BEFORE FERTILISATION. The pollen-grains are carried
by means of the wind to the ovules; these enclose the embryo-sac, and
are situated on the open fruit-leaf (carpel), which has no stigma.
Alternation of generations:
I. Prothallium = Endosperm in ovule.
II. Leaf-bearing plant, with flowers which produce the pollen-sac
and ovule.
3 Classes: 1. Cycadeæ.
2. Coniferæ.
3. Gnetaceæ.
Division V.--=Angiospermæ=. The members of this group are very
similar to those of Division IV. The ovules are, however, encased in
closed fruit-leaves (ovary), which have a special portion (stigma)
adapted for the reception and germination of the pollen-grains. The
pollen-grains are bicellular, but with only a membrane separating
the two nuclei; they are carried to the stigma by animals (chiefly
insects), by the wind, or by some other means. Endosperm is not formed
till AFTER FERTILISATION. Alternation of generations in the main as in
the Gymnosperms, but less distinct; while the sexual generation, the
prothallium, with the organs of fertilisation, is also strongly reduced.
2 Classes:[1] 1. Monocotyledones. Embryo with one seed-leaf.
2. Dicotyledones. Embryo with two seed-leaves.
For a long time the vegetable kingdom has been divided
into. CRYPTOGAMS (so called because their organs
of reproduction remained for some time undiscovered), and
PHANEROGAMS or Flowering-plants which have evident
sexual organs.
The first three divisions belong to the Cryptogams, and the
third and fourth divisions to the Phanerogams. This arrangement
has no systematic value, but is very convenient in many ways.
The Cryptogams are also known as Spore-plants, since they
multiply by unicellular organs (spores), and the Phanerogams in
contradistinction are called Seed-plants (Spermaphyta), since
they multiply by seeds, multicellular bodies, the most important
part of which is the embryo (a plant in its infancy). Mosses,
Ferns, and Gymnosperms are together known as Archegoniatæ, since
they possess in common a female organ of distinct structure, the
Archegonium.