Part 20

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.

Few of this tribe have anything like true woody texture, except their highest order, the ferns, which form some of the most beautiful objects in the vegetable world. Few of the family of acrogens are of much direct use to man, the mushroom tribes are very generally eaten where they abound, the lichens of the arctic regions form the food of the reindeer (the greatest friend of man in these cold climes) as well as, in part, the food of man himself; but although these lowly plants serve man but little, directly, there is not a shadow of doubt that they have as important an office to fulfil as any other family or tribe of organised creatures, whose purpose may meet the eye more plainly. For all the members of creation form, as it were, the links of one great chain, and were but one removed, though it might perchance be only some poor weed or lowly moss, yet might it cause the whole to be annihilated; for certain earthy matters enter into the structure of all plants, and it appears to be the wonderful office of some of these lowest tribes of plants to prepare this earthy matter for its reception into the systems of higher organisms, for as silica is one of the primitive rocks of the earth and is only found in fragments, from the largest to the sand on the sea-shore, which is nothing but a collection of minute fragments of quartz worn small by attrition, yet a grain of sand is a gigantic mass of rock in comparison with the thin porous hollow shells of the Diatomaceæ, &c., and by far too large to be absorbed or dissolved so as to be taken into the systems of other plants that may require it, which plants would cease to exist if this earth were not thus prepared for them; now these are the corn-bearing plants, the most useful to the animal world, and upon which it in reality depends for existence. Moreover the whole of the mould in which the higher orders of plants grow, is formed by the decomposition of the more humble grades, especially the lichens, which first take possession of the surface of bare rocks and stones, and furnish by their death food fit for the sustenance of those which follow them. Like the higher orders of vegetation, these minute plants excrete oxygen, and thus in the ocean may supply this vital element for the respiration of the various corresponding minute animal organisms which inhabit the depths of the sea and which cannot come to the surface to get it, so that the two thus supporting each other, form food for all the higher marine animals, which are finally eaten by man. So that upon some of these minute and apparently useless creatures hang the lives and well-being of many of the most important vegetables and animals.

Dr. Lindley divides the acrogens into the following orders:--

1. ALGÆ (Algals), including Sea-weeds, &c.

The Algæ include the lowest of all the vegetative organisms, the "Protophytes" (first plants). These have no individual parts, but consist of living cells, propagating by sub-division or by the union of two cells into one, causing the formation of "nuclei" or smaller cells within them, each of which becomes a parent cell after the rupture of the cell-membrane which contained them.

Dr. Carpenter, in his "History of the Microscope," says:--"The life-history of one of these uni-cellular plants in its most simple form, can scarcely be better exemplified than in the Palmogloea macrococca, one of those humble forms of vegetation which spreads itself as a green slime over damp stones, walls, &c. When this slime is examined with the microscope, it is found to consist of a multitude of green cells, each surrounded by a gelatinous envelope; the cell, which does not seem to have any distinct membranous wall, is filled with granular particles of a green colour, and a 'nucleus' may sometimes be distinguished through the midst of these. When treated with tincture of iodine, however, the green contents of the cell are turned to a brownish hue, and a dark-brown nucleus is distinctly shown. Other cells are seen, which are considerably elongated, some of them beginning to present a sort of hour-glass contraction across the middle; in these is commencing that curious multiplication by duplicative subdivision which is the mode in which increase nearly always takes place throughout the vegetable kingdom."

The higher tribes of Algæ embrace the sea-weeds; these are for the most part broad, leaf-like expansions of "thallus," composed of cellular tissue, they sometimes grow to an enormous length. Humboldt mentions the sea-grass as extending for miles, and forming continuous extensions of two or three hundred feet, and the Macrocystis pyrifera attains to the length of more than a thousand. The common Bladder-wrack (Fucus vesiculosus) was formerly much used to procure soda from, its ashes containing a considerable quantity, it is also used for manure; the Laminaria digitata is eaten under the name of "tangle," and a nutritious jelly is made from the "Carigeen moss" (Chondrus crispus).

2. CHARACEÆ (Charas).

These are a kind of fresh-water Algæ, composed of tubes of cellular tissue; they are peculiar, from the fact that the spores of the plant have cilia, giving to them the powers of motion and enabling them to swim away and spread the plant afar off. It is in the Charas that the peculiar circulation of the granules of "endochrome" called "cyclosis" is best seen.

3. FUNGI (Fungals), including Mushrooms, &c.

The Fungi comprise a great variety of vegetable growths, from the mould which grows on any animal or vegetable substance, to the mushroom. Some of the moulds or mildews found on various decaying substances are peculiar to them, and in many cases exceedingly destructive. The microscopic fungus Puccinea graminis, is the parasite which fixes itself to corn and produces the disease known as mildew, and the Uredo segetum (another microscopic fungus) causes the "smut;" the "bunt" is caused by the Uredo foetida, and the "spur," or "ergot," which attacks rye, is caused by the Acinula clavis. These fungi completely destroy the grain of corn, in which they form, and propagate in the most rapid manner; the ergot is moreover a dangerous poison to those who eat the bread made of rye infected by it. The Truffle (Tuber cibarium) is a kind of underground fungus, and is esteemed a dainty. Mushrooms are also fungi, and several species are sufficiently wholesome; these are the Field Mushroom (Agaricus campestris) and the Fairy-ring Mushroom (Agaricus pratensis).

4. LICHENES (Lichens),

Are those dry scaly growths forming grey, green, or yellow spots on the barks of trees and in various other places, and they grow in a sort of leaf or scale called a "thallus." They are used as articles of food and as "dye-stuffs;" the Cetraria Icelandica is the "Iceland Moss" used here for making a sort of nutritious drink or jelly, the natives of Iceland, however, use it as common food; the Cladonia rangifarina, or Reindeer Moss, is the chief food of that useful creature which forms the whole property of the Laplander; and the Roccella tinctoria is the substance from which the dye called "archil" is procured.

5. FILICES (Ferns).

The Ferns are a very numerous order of acrogenous plants, growing in the temperate regions from a rhizome or underground stalk (commonly called its root), which throws up "fronds" or leaves with a strong midrib; this midrib is commonly called its stalk, but in tropical countries the fern stalk rises above ground to the height of 30 or 40 feet, and then it is seen that the ordinary stalks are but the midribs of the fronds. There are between two and three thousand species of fern. The fronds open in a peculiar manner, unwinding as it were from a round ball. The "sorri" or seed-cases are situated at the back of the fronds in little brown spots, each of which is found to consist of a heap or collection of round capsules, and if these be placed under the microscope they have the appearance of little membraneous cases covered with net-like markings, and at the upper part a striated band of a brown colour, which after a time stretches out into a nearly straight line, tearing open the bag or capsule, and a number of seeds escape. Ferns grow best in damp and shady situations, and will thrive well in damp mould under a glass case.

6. MARCHANTIACEÆ (Liver-worts).

These Liver-worts are much like Lichens, growing between and upon stones near springs and moist places, and forming a broad thallus or root from which grow cup-shaped sporangia or seed-cases. The Marchanta polymorpha is one of its chief members.

7. JUNGERMANNIACEÆ (Scale-mosses).

The Scale-mosses grow in moist places and under the stems of trees and plants. Their appearance is scaly, and they have a sort of stalk.

8. BRYACEÆ (Urn-mosses).

Urn-mosses comprise the most ordinary of the mosses, the "Brium," which grows on the ground everywhere, forming tufts; its fructification resembles an urn, and hence its name.

9. LYCOPODIACEÆ (Club-mosses).

These are very beautiful mosses, of a bright green colour, growing in moist places. There are about 200 species of club-mosses known. The common Lycopodium is its most characteristic member. It grows well with ferns under a glass case.

10. EQUISETACEÆ (Horsetails).

The Equisetaceæ are the highest of the Acrogens, and nearly resemble the Endogens; they grow in ditches and pools, have a hollow stem with joints at regular intervals from each of which a whorl of green modified leaves arises; they are very full of earthy matter (silica), and one kind (Equisetum Hyemale), called Dutch Rush, is so rough with it that it is used for polishing and scraping many articles.