Fig. 45.—Part of the flower-head of the Burdock. part of the flower of the common Bur or Burdock (Arctium Lappa), so annoying from the strong hold it takes of any part of the dress which it may chance to touch. In fig. 45 a is the involucre, every scale in which is hooked and turned inwards, so as to hold firmly whatever it may catch; b is a floret showing its tubular shape, and its style proceeding through the united anthers; c shows the hardened bracts or paleæ, the other florets having been removed; and d shows a fruit with a palea attached, magnified. All the different kinds of thistle belong to this division; and though many of the kinds have not the hardened bracts, they have all a spiny involucre. The pappus of the thistle is generally attached to a kind of disk, from which it becomes loosened soon after the seed falls, and this thistle, down, as it is called, being extremely light, is blown about by the winds. All the thistles have fleshy roots, and take firm hold of the soil. The Corn Blue-bottles (Centaurea), the Wild Saffron (Carthamus tinctoria), and many other well-known plants, belong to this division.
TRIBE III.—CORYMBIFERÆ.
Florets partly tubular and partly ligulate; juice watery; sometimes bitter and tonic, and sometimes acrid. The seeds of some of the species yield oil.
The plants included in this tribe all bear more or less resemblance to the common Daisy. In this well-known flower, the white florets are all ligulate, and compose what is called the ray, and the yellow flowers, which are tubular, are called the disk. The involucre is simple and leafy, and the receptacle is conical. The seeds are without pappus. The Chrysanthemum is nearly allied to the Daisy, and its seeds also are destitute of pappus; but it is easily distinguished by its involucre, which is scaly, and by the flower forming a kind of depressed globe in the bud. The scales of the involucre are strongly marked, from being edged with a thin membrane, and the florets of the ray are much longer in proportion to those of the disk than in the Daisy. The great Ox-eye Daisy, which was formerly called Chrysanthemum leucanthemum, is now placed in a new genus, and called Leucanthemum vulgare; and the Chinese Chrysanthemums have been removed to the genus Pyrethrum. Both plants, however, will no doubt long continue to be called by their old names. The beautiful yellow-flowered plant often found growing among corn (Chrysanthemum segetum), the three-coloured Chrysanthemum (C. tricolor or carinatum), and the yellow annual Chrysanthemum (C. coronarium), with some others, have been left by Professor De Candolle in their old genus. In the Feverfew (Pyrethrum), the receptacle is elevated, and the fruit is crowned with a narrow membrane. The Pellitory of Spain was formerly considered to belong to this genus, and afterwards to the Chamomile, but it is now called Anacyclus Pyrethrum. Matricaria Chamomilla, the wild Chamomile, has also no pappus; and in this plant the receptacle is almost cylindrical. The true Chamomile (Anthemis nobilis) greatly resembles the Chrysanthemum in its flowers; but they are distinguished by having a chaffy receptacle, and the fruit having a membranous margin. The smell of the Chamomile is aromatic, and its qualities highly tonic. The Yarrow (Achillea millefolium) is another plant destitute of pappus, but with a chaffy receptacle; it is also remarkable for its leaves, which are doubly pinnatifid.
It will be seen by the above enumeration, that in many plants belonging to this division, the pappus is entirely wanting, and in others it will be found to assume a different form to that which it bears in the other tribes. Thus, in the Bur-Marigold (Bidens), the pappus consists of from two to five erect awns, which are covered with very small, bent bristles. The genus Senecio has soft, hairy pappus, as may be seen in the common Groundsel (S. vulgaris); the leaves of this weed are pinnatifid, and somewhat stem-clasping, and the flowers have no ray florets. In other species of this division, however, the ray florets are very conspicuous: as, for example, in the common yellow Ragwort (S. Jacobæa), in the great fen Ragwort, or Bird’s tongue (S. paludosa), and in the purple Jacobæa (S. elegans). Nearly allied to Senecio, is the genus Cineraria, so much, indeed, that Professor De Candolle, in his late arrangement of the Compositæ, has included the greater part of the species in Senecio. The greenhouse species, with purple flowers, are among those which have been changed; but they will probably always retain the appellation of Cineraria, as an arbitrary English name. The Asters, or Michaelmas Daisies, Golden Rod, Elecampane, Leopard’s Bane, the Cape Marigold, (now called Dimorphortheca, instead of being included in the genus Calendula), Coltsfoot, Wormwood, Southern-wood, Tansy, and many other well-known plants, belong to this division.
The Sunflower (Helianthemum annuus) is an example of one of the plants belonging to this division which has seeds yielding oil. In this plant the pappus is awl-shaped, and deciduous; and the receptacle, which is broad and somewhat convex, is paleaceous. The seeds are large and oblong, and when pressed, yield a considerable quantity of oil. The Madia is another oil plant; and indeed the seeds of several in this division yield oil.
TRIBE IV.—LABIATÆFLORÆ.