Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/130

Rh 120 BOTANY [REPRODUCTIVE ORGANS. applied closely to the calyx, and may thus be confounded with it, as in Malvaceae and species of Dianthus and Eranthis, where they have received the name of epicalyx or calyculus. In some Rosaceous plants an epicalyx is present, due to the formation of stipulary structures by the sepals. In many cases bracts seem to perform the function of protective organs, within or beneath which the young flowers are concealed in their earliest stage of growth. When bracts become coloured, as in Amherstia nobilis, Euphorbia splendens, Erica elegans, and Salvia splendens, they may be mistaken for parts of the corolla. They are sometimes mere scales or threads, and at other times they are abortive, and remain undeveloped, giving rise to the ebracteated inflorescence of Cruciferse and some Boraginacese. Sometimes no flower-buds are produced in their axil, and then they are empty. A series of empty coloured bracts terminates the inflorescence of Salvia Horminum. The smaller bracts or bracteoles, which occur among the sub divisions of a branching inflorescence, often produce no flower-buds, and thus anomalies occur in the floral arrange ments. Bracts are occasionally persistent, remaining long attached to the base of the peduncles, but more usually they are deciduous, falling off early by an articulation. In some instances they form part of the fruit, becoming incorporated with other organs. Thus, the cones of Firs and the strobili of the Hop are composed of a series of bracts arranged in a spiral manner, and covering fertile flowers ; and the scales on the fruit of the Pine-apple are of the same nature. In amenta or catkins the bracts are called squamae or scales. At the base of the general umbel in Umbelliferous plants, a whorl of bracts often exists, Plate VII. called a general involucre, and at the base of the smaller umbels or umbellules there is a similar leafy whorl called involucel or partial involucre. In some instances, as in Fool s-parsley, there is no general involucre, but simply an involucel ; while, in other cases, as in Fennel, neither involucre nor involucel is developed. In Composite the name involucre is applied to the leaves, scales, or phyllaries, surrounding the head of flowers (lig. 146, i), as in Plate IX. Dandelion, Daisy, Artichoke. This involucre is frequently composed of several rows of leaflets, which are either of the same or of different forms and lengths, and often lie over Fig. 147. Fig. 146. Fio. 146. -Head (capitulum) of Marigold (Calendula), allowing a congeries of flowers, enclosed by rows of bracts or phyllaries, f, at the base, which are col lectively called an involucre. Fio. 147. Fruit of the Oak (Quei-cus pedunculata), showing a collection of bracts, a, forming the cup (cupula) of the acorn t. each other in an imbricated manner. When the bracts are arranged in two rows, and the outer row is perceptibly smaller than the inner, the involucre is sometimes said to be caliculate, as in Senecio. The leaves of the involucre are spiny in Thistles and in Dipsacus, and hooked in Burdock. Such whorled or verticillate bracts may either remain separate (polyphyllous), or may be united by cohesion (gamophyllous), as in many species of Bupleurum, and in Lavatera. In Composites besides the general envelope called the involucre, there are frequently chaffy and setose bracts at the base of each flower, and in Dipsacacese a membranous tube surrounds each flower. These structures are of the nature of an epicalyx. In the acorn the cupula or cup (fig. 147, a} is formed by a growing upwards of the flower- stalk immediately beneath the flower, upon which scaly or spiny protuberances appear. It is of the nature of bracts. Bracts also compose the husky covering of the Hazel-nut. In the Yew the succulent covering of the seed is by some considered to be formed by the bracts. When bracts become united together, and overlie each other in several rows, it often happens that the outer ones do not produce flowers, that is, are empty or sterile. In the Artichoke the outer imbricated scales or bracts are in this condition, and it is from the membranous white scales or bracts (paleod) forming the choke attached to the edible receptacle that the flowers are produced. The sterile bracts of the Daisy occasionally produce capitula, and give rise to the Hen-and-Chickens Daisy. In place of developing flower- buds, bracts may, in certain circumstances, as in proliferous or viviparous plants, produce leaf -buds, and the flower-buds, like the leaf -buds, may be terminal or they may be lateral. A sheathing bract en closing one or several flowers is called a spatha or spathe. It is common among Monocotyledons, as Narcissus (figure 148), Snow - flake, Arum, and Palms. In some Palms it is 20 feet long, and en closes 200,000 flowers. It is often associated with that form of inflorescence termed the spadix, and may be coloured, as in Richardia sethiopica, some times called the ^Ethiopian or Trumpet Lily. When the spadix is compound or branching, as in Palms, there are smaller spathes, ^ig. 148. surrounding separate parts nowerB O f Polyanthus Narcissus (Sareiiuu of the inflorescence, to Tazetta ) bursting from a sheathing bract which the name spathellce has sometimes been given. The spathe protects the flowers in their young state, and often falls off after they are developed, or hangs down in a withered form, as in some Palms, Typha, and Pothos. In Grasses the outer scales of the spikelets have been considered as sterile bracts, and have received the name of glumes (fig. 149, gl) ; and in Cyperaceae bracts enclose the organs of reproduction. Bracts are frequently changed into complete leaves. This change is called phyllody of bracts. It is seen in species of Plantago, especially in the variety of Plantago media, called the Rose-plantain in gardens. In this plant the bracts become leafy, and form a rosette round the flowering axis. Similar changes occur in Plantago major, P. lanceolata, Ajuga reptans, the Dandelion, the Daisy, the Dahlia, and in Umbelliferous plants. The conversion of bracts into stamens has been observed in the case of Abies excelsa. This has been called staminody of bracts. A lengthening of the axis of the female strobilus of Coni ferae is not of infrequent occurrence in Cryptomeria japonica, Larix europsea, &c., and this is usually associated with a leaf -like condition of the bracts, and sometimes even with the development of leaf-bearing shoots in place of the scales.