The seed is the ovule ripened, it contains the germ of the future plant, called the "embryo," the outer part of the seed is called the "testa," and the space between this and the embryo is generally filled with starchy matter called the "albumen." The embryo consists of the plumule or stem, the "radicle" or root, and the cotyledons or leaves of the future plant; when the seed has but one cotyledon it is called "monocotyledonous" and when it has two "dicotyledonous."

Flowers are arranged in various ways upon the plants which produce them, and receive names accordingly; the whole arrangement of flowers is called the "inflorescence."

The following are the principal forms of inflorescence:—

Hemlock. The Umbel, in which all the flower-stalks (pedicels) radiate from one point, as in the carrot (daucus carota). Umbels are sometimes compound, that is, the flowers are placed in umbels at the end of stalks themselves radiating from a point and so forming an umbel, as in the Hemlock (Conium maculatum).
Plantain. The Spike, is that kind of infloresence in which all the flowers are seated without stalks upon a general peduncle or axis, as in the Plantain (Plantago media), in which the spike is entire, or as the Lavender (Lavandula Vera), in which the spike is interrupted, that is, the inflorescence is not continuous.
Hazel. Catkin, or Amentum, is the same as a spike, but in which the flowers are imperfectly developed, as in the Hazel (Corylus), Willow (Salix), White Poplar (Populus Alba), &c.
Water-cress. The Raceme has the inflorescence placed along a common axis or centre, the same as a spike, but with the flowers placed upon stalks instead of being sessile, as in Water-cress (Nasturtium officinale) and Red Currant (Ribes rubrum).
Candy-tuft. The Corymb is a form of inflorescence pretty much the same as raceme, but the flowers of which proceed upwards till they are all on a level, as in Candy-tuft (Iberis).
Creeping Soft Grass. The Panicle, the same as the raceme, but having the flower stalks themselves divided into branches, as in Creeping Soft Grass (Holcus mollis). This and the spike are the most usual form of inflorescence found among grasses, in many of which the panicle, however, is often contracted almost to a spike.
Elder. The Cyme, this resembles the panicle shortened in such a manner as to become flattened or almost corymbose, as in the Elder Tree (Sambucus nigra), in which there are five principal stalks of inflorescence.
Chamomile. Capitulum, in which the flowers arise from a broad round head or receptacle as in the composite flowers, such as Chamomile (Anthemis nobilis); in such flowers the star-like ray of florets are called the florets of the ray, and those composing the centre the florets of the disc.
Arum. The Spadix is that form of inflorescence in which the expanded bract, called a spathe, forms a sort of sheath inclosing the flowers. This spathe is white in the example given, and is often mistaken for part of the flower itself, as in the Wake-robin or Arum (Arum maculatum).

The vegetable kingdom is divided into three great natural families, the Acrogenæ, the Endogenæ, and the Exogenæ.

The acrogenous plants are those which as a general rule have neither branches, leaves, nor flowers; they are almost wholly made up of cellular tissue, and are many of them so minute that they are quite invisible individually to the unassisted eye, and are among the most wonderful works of the Creator, having an amount of beauty in form and elaboration of ornament bestowed on them, quite equal to anything among the higher and larger creations, and yet some of these are so small that tens of millions may be placed in the space of a cubic inch, of such are the Diatomaceæ and Desmidiaceæ.

The acrogens take an immense range in the scale of organisation, from the ferns (which appear but little inferior to the exogenæ or endogenæ, have stems and leaves, and in some cases, as in hot and moist climates, assume the size and form of a tree), to the very lowest state of vegetable existence, consisting of simple cells uniting into strings or forming simple threads, such as the green algæ which form on stagnant waters and damp ground or wood-work, and the mould or mildew which forms on all decomposing substances. The general name for these acrogens, "cryptogamia," which has been in use for a long time and is commonly still used, indicates that the reproductive organs are invisible, hence the expression used by one of Shakespeare's characters, "We have the secret of fern seed, we walk invisible;" but this is not really the case, for the "sorri" at the back of fern-leaves, are vessels filled with spore cases each having a number of angular seeds within it; the lower tribes of the acrogens do not commonly grow from seed but by an extension of their several parts by the development of the cells of which they are composed, and by their separation into portions.