Page:Flora Hongkongensis.djvu/39

Rh a Panicle, or paniculate, when the axis is divided into branches bearing two or more flowers.

a Head, or capitate, when several sessile or nearly sessile flowers are collected into a compact head-like cluster. The short, flat, convex or conical axis on which the flowers are seated, is called the receptacle, a term also used for the torus of a single flower (135). The very compact flower-heads of Compositœ are often termed compound flowers.

an Umbel, or umbellate, when several branches or pedicels appear to start from the same point and are nearly of the same length. It differs from the head, like the raceme from the spike, in that the flowers are not sessile. An umbel is said to be simple, when each of its branches or rays bears a single flower; compound, when each ray bears a partial umbel or umbellule.

a Corymb, or corymbose, when the branches and pedicels, although starting from different points, all attain the same level, the lower ones being much longer than the upper. It is a flat-topped or fastigiate panicle.

a Cyme, or cymose, when branched and centrifugal. It is a centrifugal panicle, and is often corymbose. The central flower opens first. The lateral branches successively developed are usually forked or opposite (dichotomous or trichotomous), but sometimes after the first forking the branches are no longer divided, but produce a succession of pedicels on their upper side forming apparently unilateral centripetal racemes; whereas if attentively examined, it will be found that each pedicel is at first terminal, but becomes lateral by the development of one outer branch only, immediately under the pedicel. Such branches, when in bud, are generally rolled back at the top, like the tail of a scorpion, and are thence called scorpioid.

a Thyrsus, or thyrsoid, when cymes, usually opposite, are arranged in a narrow pyramidal panicle.

75. There are numerous cases where inflorescences are intermediate between some two of the above, and are called by different botanists by one or the other name, according as they are guided by apparent or by theoretical similarity. A spike-like panicle, where the axis is divided into very short branches forming a cylindrical compact inflorescence, is called sometimes a spike, sometimes a panicle. If the flowers are in distinct clusters along a simple axis, the inflorescence is described as an interrupted spike or raceme, according as the flowers are nearly sessile or distinctly pedicellate; although when closely examined the flowers will be found to be inserted not on the main axis, but on a very short branch, thus, strictly speaking, constituthig a panicle.

76. The catkins (amenta) of Amentaceœ, the spadices of several Monocotyledons, the ears and spikelets of Grasses are forms of the spike.

77. Bracts are generally placed singly under each branch of the inflorescence, and under each pedicel; bracteoles are usually two, one on each side, on the pedicel or close under the flower, or even upon the calyx itself; but bracts are also frequently scattered along the branches without axillary pedicels; and when the differences between the bracts and bracteoles are trifling or immaterial, they are usually all called bracts,

78. When these bracts appear to proceed from the same point, they will, on examination, be found to be really either one bract and two stipules, or one bract with two bracteoles in its axil. When two bracts appear to proceed from the same point, they will usually be found to be the stipules of an undeveloped bract, unless the branches of the inflorescence are opposite, when the bracts will of course be opposite also.

79. When several bracts are collected in a whorl, or are so close together as to appear whorled, or are closely imbricated round the base of a head or umbel, they are collectively called an Involucre. The bracts composing an involucre are described under the names of leaves, leaflets, bracts, or scales, according to their appearance. Phyllaries is a useless term, lately introduced for the bracts or scales of the involucre of Compositœ. An Involucel is the involucre of a partial umbel.

80. When several very small bracts are placed round the base of a calyx or of an involucre, they have been termed a calycule, and the calyx or involucre said to be calyculate, but these terms are now falling into disuse, as conveying a false impression.

81. A Spatha is a bract or floral leaf enclosing the inflorescence of some Monocotyledons.