590 PLANT symmetry of thoir parts, the lily for example, are only disfigured by becoming double. Doub- ling is most frequently produced by the con- version of the stamens into petals ; but in many cases it is due to the production of two or more petals in the place of one, and there are double flowers which neither of these causes fully ac- counts for. Doubleness is regarded as indica- ting a tendency to sterility, and whatever dis- turbs the reproductive functions tends to pro- duce double flowers ; fertility is diminished by a variety of causes, and long cultivation in a rich soil is one of the most common. When any derangement of the forces of the plant causes the stamens to be sterile, they revert to petals; when this once takes place, the flower "breaks," as the gardeners say, the ten- dency becoming hereditary ; seedlings from a plant thus changed are in some cases likely to show a greater departure from the normal condition, and by continuously selecting seeds from those in which the tendency to become double is strongest, the habit may be fixed; finely doubled flowers have been produced in this manner from one in which only a single extra petal appeared. The stamens become sterile first, and a flower may have all of its stamens converted into petals, while the pis- til is still fertile ; such flowers fertilized by the pollen from a single or partially double one will yield seeds with a strong tendency to pro- duce double flowers. When the metamorpho- sis is carried so far as to involve the pistils, the plant can only be propagated by cuttings or other subdivision. The doubling in flow- ers of composites is not due to a change in the stamens; in the natural state of the dahlia, sunflower, and others, there is a disk of small tubular flowers, surrounded by a ray of much larger flat and showy ones ; these flowers are regarded as double when the tube-shaped co- rollas of the disk are developed like those of the ray. The Poimettia has been mentioned as a plant cultivated for the showy bracts which surround a cluster of small inelegant flow- ers; a double variety of this was discovered by Roezel in Mexico ; in this the flowers are changed into leafy branches, and these leaves are colored like the ordinary large bracts, ex- hibiting a large mass of brilliant color with- out any flower at all being concerned. The Fruit. This has already been described as the ripened (simple or compound) pistil, and such accessory organs as remain attached to it. The changes the pistil undergoes in maturing are often very striking; one of these is a great increase in size ; another frequent change is in the tissues, which may become exceedingly pulpy and soft, or on the other hand may be indurated and even become bony. Another marked change occurs in the substance; the pistil, which at first was essentially the same in composition as a leaf, as it enlarges be- comes, as in the grape, charged with acid, or in the persimmon with tannin, and as the fruits reach maturity the acidity or astrin- gency gives place to sweetness, indicating the formation of sugar. The interior structure of the pistil is sometimes not to be traced in the fruit; the number of cells may be diminished, or by the formation of false par- titions increased ; the number of seeds per- fected is often fewer than the ovules; while the peach, almond, and their allies always have two ovules in the ovary, but one gen- erally becomes a seed, though both some- times develop, as " double-meated " almonds and peach stones are not rare. In the oak the ovary has three cells with two ovules in each cell ; in ripening the three divisions are obliterated, and five ovules perish, as we find the acorn to be only a one-celled, one-seeded fruit. A few examples drawn from familiar plants will illustrate the changes the pistil un- dergoes in becoming a fruit. One of the im- portant characters in descriptive botany is the dehiscence, or way in which the fruit opens ; many fruits, both simple and compound, are indehiscent, but in other cases fruits of both kinds open to let out the seed ; the dehiscence in a simple carpel may be along the ventral suture, or by both sutures ; and in a compound fruit the carpels may open upon the back, or they may break away from- one another and open by the ventral suture ; there are several anomalous forms of dehiscence which seem to bear no relation to the structure of the pistil, as where the fruit opens by a regular lid. The ripened ovary, or the wall of the fruit what- ever changes it may undergo, is the pericarp. In the common buttercup the fruit is small, dry, one-seeded, and indehiscent ; such fruits are akenes ; the proper fruit of the strawberry is of this kind, the edible portion being the en- larged receptacle. The fruit of the columbine, paeony, and larkspur results from simple pis- tils ; these open at the ventral suture and ex- pose the numerous seeds ; such a fruit is a fol- licle, from which to the legume or pod is but a step ; in the pea it is dehiscent by both sutures, and the carpel falls apart in two valves ; in the pea the pericarp still retains something of its leafy character, and in the common bladder- nut the walls become very thin and papery, and before they are fully matured are striking- ly leaf -like. The most remarkable change in a simple pistil is seen in the drupe, of which tl almond, peach, plum, cherry, and others known as stone fruits, are examples ; in these the car- pellary leaf undergoes two very unlike chan- ges; the interior portion of the ovary, th* corresponding to the upper part of the leaf, the fruit matures has its cells filled up by a de posit which makes them nearly solid, and tissue which they form, the stone of the fruit exceedingly hard and bony ; while this is going on the outer portion, or the under side of tl leaf, increases greatly in thickness and becomt fleshy, juicy, and edible, as in the peach and others, while in the almond, though it becomes thick, it is hard and dry. The stone (puta- men) in these fruits is not a part of the seed,
