The Vegetable World: Being a History of Plants, with Their Botanical Descriptions and Peculiar Properties

each lobe in the Barberry, and two for each lobe in the Persian Laurel, as represented in the engravings. A familiar acquaintance with the microscopic structure of the

Fig. 193. Fig. 194. Fig. 195. Stamens of Solanum, Barberry, and Persian Laurel.

pollen of vegetables gives rise to some very curious speculations. en a microscope of considerable power is employed, we find that the forms of these grains vary very considerably in different species, some of their forms being of a very elegant description.

The pollen-grain is generally composed of a sort of double covering, the innermost containing a mucilaginous liquid, named Horilla. Figs. 196 and 197 are the pollen-grains of the Hollyhock; having a sort of double sac or covering surrounding each graim- The external membrane of the globule of pollen is smooth, dotted, granulated. It is covered with small prickles, or finely reticulated, according to the species. It also exhibits folds and pores. In the pollen of Wheat (Fig. 198) there is only one pore; in the Primrose-tree (Fig. 199) there are three. Figs. 200, 201, and 202 show the pollen grains of Garlick, the Phlox, and the Melon. The number of pores in a pollen-grain may reach five or even eight. These pores perform important functions, as we shall soon see. When a grain of pollen is placed in water it swells, because it absorbs a certain quantity. of the liquid. Its membranes expand, and the internal one protrudes through the pores of the external membrane. The vessel bursts, and the florilla escapes in a sort © mucous and granulous jet. This is an anomalous but very curious phenomenon to observe. It is anomalous, because it is not thus

that the matter takes place in nature. When a pollen-grain falls on the moist and viscous surface of the pistil, which we shall soon describe, and which bears the name of stigma, it expands slowly, appearing to absorb its humidity; the interior mem-

Pee. Fee eaecon velope. ql Pollen of the Holy- port ‘ollen of Wheat. ock, first Envelope.

Of Peibee aa OF Gantio. on Phiox. oftheSedan

brane becomes gradually extended and protruded through one or two pores in the exterior coating, in the form of delicate tubular protrusions, which lengthen by degrees, and end by forming real tubes, called pollen-tubes.

The length of these tubes varies considerably; they attain in certain cases many hundred times that of the pollen-grain, which gave it birth. This prodigious lengthening evidently ot p 1 from a mere elongation of the internal membrane of the pollen-grain, but is the result of an actual growth in this membrane. The pollen-tube is nourished and grows, that is to say, it vegetates; So that, leaving the stigma, it penetrates into the tissues, which it is intended to traverse. We shall have occasion to return to the pollen-tube when we speak of fecundation in the next section.

Although pollen-grains are almost always free and distinct, there are some plants in which these grains are joined together, and often very closely. In the Orchidacee (Fig. 203), the pollen is gathered together into masses, sometimes almost pulverulent, with loosely-cohering granules; sometimes it is formed of numerous small angular masses, joined together by means of glutinous L 2

matter. In Plantanthera chloranta, and Asclepias floribunda, the masses of pollen show the arrangement as represented by Figs. 204 and 205.

The number of stamens in each flower varies according to the

Fig. 203.—Pollen Mass + ~ Fig. 204.—P Fig. 205.—Pollen Mass in Orchis maculata. five Meera of Ancheeliad floribunda. species. When they are arranged in whorls, they are generally definite in number, as in the Vine (Fig. 206), and the Primrose, which have five. When they are in a spiral, they are usually very numerous, as in the Magnolia and the Ranunculus. Stamens may be all of the same height, as we see in the Lily, Tulip, and Barrage, or else very unequal. In the Geranium, there are five

Hig, 206—Androceum Stamensofthe Vine. stamens bigger than the others, which are also five in number. In the Wallflower (Fig. 207), which has six stamens, four are bigger than the others; Linnxus called these tetradynamous. In the Snap-dragon (Fig. 208), there are four stamens, two of which are larger than the others; Linnzus called them didynamous stamens.

The stamens of the same flower may be completely independent one of the other, or more or less united either by their filaments or by their anthers. In the Mallow (Fig. 209), and in the Flax plant, all the stamens are united to each other by their filaments in a single bundle. In the French Bean, and the Milk-worts, they

are united in two bundles; inthe Egyptian St. John’s Wort (Fig. 210),

Fig. 207.—Androceeum Fig. 208.—Androceum Fig. 209.—Androceum of the Wallfiower. of the Snap-dragon. of the Mallow.

in three bundles; in the Ricinus (Fig. 211), in several bundles.

Fig. 211.—Stamens of 6 B10, Fig. 210.—Androczenm of St. John’s Wort. Ricizus (Castor-Oil-tree).

After Linnzus, the stamens are called monadelphous, iadelphous, triadelphous, polyadelphous, as they form one, two, three, or more bundles. In the Dandelion, Artichoke, and Thistle, the stamens are joined together by their anthers, so as to form a kind of tube, supported by free filaments: these are said to be synantherous (Fig. 212).

Finally, stamens may form adhesions with the floral envelopes. In the Squill, for instance, six stamens adhere by their base to the six divisions of the flower. In the Primrose, five stamens are attached to the tube of the corolla, which is monopetalous. iynanthesove Stamens.

We shall conclude our remarks on the stamens by some inquiry into the morphological nature of this part of the flower.

Bracts, sepals, and petals are modified leaves, as we have seen. It appears difficult to believe, at first sight, that the same should be the case with stamens. Yet, pick the petals from a flower of the White Water-Lily; you will observe, as you approach the centre of the flower, that the petals diminish in length and breadth, and: present towards the summit, an anther, at first rudimentary; this becomes more and more complete as the supporters pass insensibly from the form of a petal to that of a filament. In the Columbine, under the influence of cultivation, we see the stamens changing by degrees into forms analogous to those constituting its elegant corolla. In the Rose, we often find organs which are half petal and half stamen.

There is a very curious monstrosity in one species of the Rose, in which all the organs of the flower are transformed into leaves, so as to constitute what horticulturists call a monster rose. In this production we can follow, step by step, all the transformations between an almost perfect stamen, and a petal which has been transformed into a green leaf.

All these facts demonstrate that the stamen is only a metamorphosed petal. But we have already shown the analogy of petals with sepals, of sepals with bracts, and of bracts with leaves.

Stamens, therefore, like these organs, are only metamorphosed leaves. In short, the filament of the stamen has been compared to the claw of the petal, or the petiole of the leaf, the limb to the leaf itself, the pollen to a special modification of the parenchyma of the te the connective to the central part, that is, the midrib of the leaf. '

Tue Pisriu.

As we advance in the study of the organic parts of plants, it her essentialwill be observed, that nature is constantly approaching

object, the propagation and preservation of the species. The pistil is the essential organ in the reproduction of plants; Nature, there, fore, has taken care to collect round the pistil all possible means for its protection and defence. It is placed in the centre of the flower, sheltered under several concentric coverings, and defended

besides, externally, by the filaments of the stamens, which form a rampart round it. These various floral envelopes last as long as the pistil needs their protection and shelter. They disappear after fecundation, when the ovary is strengthened by its own proper development. The pistil is the female organ in vegetables, the gyne@cium, as it is sometimes called, as opposed to the androceum, the name which designates the whole of the stamens, or the male organ.

The zecium presents one of the most remarkable applications of the doctrine of vegetable metamorphosis, made popular by Goéthe, the celebrated German poet, and also a profound naturalist. We can easily understand the structure, origin, and arrangement of the gynecium, if we consider it as constituted by the transformation of a single leaf, or rather as resulting from the union, blending, and combination of several leaves in one single organ.

The elementary organs, the junction of which forms the pistil, are called by De Candolle, carpels. The carpel is to the pistil what the sepal is to the calyx, the petal to the corolla, and the stamens to the androceum. The union of the carpels generally forms the pistil, as the union of the petals form the corolla, and the union of the stamens the androceeum. Sepals, petals, and stamens, are only modified leaves; it is just the same with the carpel, which takes its rise during the phases of ia remit by the metamorphosis of the leaves.