Page:The American Cyclopædia (1879) Volume XIII.djvu/605

 PLANT 589 leaves and in no wise attached to the flower. In many cases it is impossible to distinguish between calyx and corolla; where there are many series of these parts, as in calycanthus, it is very difficult to say which is calyx and which corolla; some of the double camellias of the greenhouse show this in a striking man- ner, and in the magnolia calyx and corolla are only to be distinguished by position. In the green rose the place of the petals is occupied by a cluster of green leaves. In many flowers the petal is narrowed at the base into a claw, which corresponds to the petiole of the leaf, and this is sometimes, as in the pink, very conspicuous ; petals with a manifest claw cor- respond to petioled, and those without it to sessile leaves. The stamen shows much less resemblance to the leaf than do the sepal and petal. The filament represents the petiole or stalk of the leaf, and the theoretical structure of the anther is that it corresponds to the blade of the leaf with its edges curved in toward the midrib to form the two cells of which most anthers consist ; the midrib of the leaf is the connective ; the cellular tissue of the leaf un- dergoes marked changes and is developed as pollen. The stamens are frequently trans- formed into petals, which are undoubted leaf- like organs, as may be seen in any partly dou- ble rose and many other semi-double flowers; if stamens are visible in a double rose, it is generally easy to find bodies in every interme- diate state, from a nearly perfect petal with the vestiges of an anther upon its edge, a body half petal and half stamen, to a nearly perfect sta- men with a fragment of petal developed upon it. The double columbine of the gardens af- fords a still more striking illustration ; in this flower the petals are in the form of a hollow curved spur, and the stamens may be found with a filament, but bearing in place of the an- ther one of these curved petals. The rose often shows a complete series of transformation from the calyx to the stamen : first perfect sepals, vyithin these petals with a green midrib or par- tially changed to sepals, then perfect petals, and within these the intermediate states be- tween petal and stamen. The double rose is a flower in an abnormal state, but we find simi- lar gradations in wild flowers unchanged by cultivation ; a striking example of this is shown in the white water lily (nymphcea), in which the calyx is green on the outside and petal-like within ; within this are several series of petals, some of the inner ones with an abortive an- ther at the tip, and so on toward the centre, the petal gradually disappearing and the anther more perfectly developed, until true stamens are found bearing no resemblance to petals. In some compound pistils it is difficult to trace any resemblance to the leaf, but when the pis- tils or carpels are distinct, especially in flow- ers with a solitary pistil, the foliaceous charac- ter is manifest. It is not difficult to see that the pistil of our typical flower, or that of the larkspur, pseony, or the common pea, may be 668 VOL. xiii. 38 I formed by folding the edges of a leaf together and uniting them to form a hollow sac or pouch ; ^that this is the real nature of the sim- ple pistil may often be seen in the double cherry, in which the retrograde metamorpho- sis is strikingly exhibited, an infolded leaf ac- tually standing in place of the pistil, its pro- longed midrib, the style, bearing the knob-like stigma at the end. Other plants afford illus- trations of the same point, especially an alpine strawberry, which produces all parts of the flower, even the stamens, as green foliaceous bodies, and the pistil, though minute, as a bud of overlapping leaves. Taking this view of the simple pistil, that it is an infolded carpel- lary leaf, several theories have been proposed as to the nature of the ovule, and the subject has given rise to much discussion. Schleiden regards the ovules as buds produced upon the edges of the carpellary leaf, and the placenta as a cellular growth from its margins ; though the edge of a leaf is an unusual place for buds to appear, some plants naturally produce them there, especially Iryophyllum, which propa- gates itself from buds upon the leaf. This view of the homology of the ovule is support- ed by the fact that a number of abnormal pis- tils have been observed in which leaf buds appear in the place of ovules ; a case of this kind is a monstrous columbine, in which the simple pistils develop as flat leaves, and bear leaf buds upon their edges. Accepting this view of the structure of the simple pistil or carpel, that part of it which corresponds to the midrib of the leaf is the dorsal suture, and the union of the edges of the leaf forms the ven- tral suture, the placenta being always borne here. When two or more simple pistils are united, it is by their ventral sutures, and the collective placentae will be in the centre ; the placenta is sometimes free in the axis of the compound ovary, a state of things often caused by the obliteration of the dissepiments or divi- sion walls. In many compound ovaries the pla- centae are parietal, or upon the sides of the ovary ; a pistil of this kind is regarded as com- posed of several carpellary leaves, which, in- stead of infolding and uniting in the manner already described, are placed in a circle and joined by their contiguous edges ; the placenta in this case, instead of being composed of two edges of one carpellary leaf, is formed by the edges of two different adjacent leaves. By the projection of the parietal placentae toward the centre of the ovary a great variety of forms are produced, some of which are quite puzzling. Double Flowers. These, to which frequent reference has been made, rarely appear in na- ture, though those having normally more than one series of petals may sometimes be taken for such. In horticulture a flower is regarded as double when its proper number of petals is much increased ; in many cases the beauty of the flow- er is greatly enhanced by doubling, as in the rose ; but those flowers the beauty of which is largely dependent upon the regularity and