Fig. 112.—Calycifloræ, Opuntieæ (Passiflorinæ). A, flower of a cactus, Mamillaria (Cactaceæ) (from “Gray’s Structural Botany”). B, leaf and flower of a passion-flower, Passiflora (Passifloraceæ), × ½. t, a tendril. C, cross-section of the ovary, × 2. D, diagram of the flower.
The fourth order (Passiflorinæ) are almost without exception tropical plants, only a very few extending into the southern United States. The type of the order is the passion-flower (Passiflora) ([Fig. 112], B), whose numerous species are mostly inhabitants of tropical America, but a few reach into the United States. The only other members of the order likely to be met with by the student are the begonias, of which a great many are commonly cultivated as house plants on account of their fine foliage and flowers. The leaves are always one-sided, and the flowers monœcious.[13] Whether the begonias properly belong with the Passiflorinæ has been questioned.
Fig. 113.—Calycifloræ (Myrtifloræ, Thymelinæ). A, flowering branch of moosewood, Dirca (Thymelæaceæ), × 1. B, a single flower, × 2. C, the same, laid open. D, a young flower of willow herb, Epilobium (Onagraceæ), × 1. The pistil (gy.) is not yet ready for pollination. E, an older flower, with receptive pistil. F, an unopened bud, × 1. G , cross-section of the ovary, × 4. H, a young fruit, × 1. I, diagram of the flower. J, flowering branch of water milfoil, Myriophyllum (Haloragidaceæ), × ½. K, a single leaf, × 1. L, female flowers of the same, × 2. M, the fruit, × 2.
The fifth order (Myrtifloræ) have regular four-parted flowers with usually eight stamens, but sometimes, through branching of the stamens, these appear very numerous. The myrtle family, the members of which are all tropical or sub-tropical, gives name to the order. The true myrtle (Myrtus) is sometimes cultivated for its pretty glossy green leaves and white flowers, as is also the pomegranate whose brilliant, scarlet flowers are extremely ornamental. Cloves are the dried flower-buds of an East-Indian myrtaceous tree (Caryophyllus). In Australia the order includes the giant gum-trees (Eucalyptus), the largest of all known trees, exceeding in size even the giant trees of California.
Among the commoner Myrtifloræ, the majority belong to the two families Onagraceæ and Lythraceæ. The former includes the evening primroses (Œnothera), willow-herb (Epilobium) ([Fig. 113], D), and fuchsia; the latter, the purple loosestrife (Lythrum) and swamp loosestrife (Nesæa). The water-milfoil (Myriophyllum) ([Fig. 113], J) is an example of the family Haloragidaceæ, and the Rhexias of the eastern United States represent with us the family Melastomaceæ.
The sixth order of the Calycifloræ is a small one (Thymelinæ), represented in the United States by very few species. The flowers are four-parted, the calyx resembling a corolla, which is usually absent. The commonest member of the order is the moosewood (Dirca) ([Fig. 113], A), belonging to the first of the three families (Thymelæaceæ). Of the second family (Elæagnaceæ), the commonest example is Shepherdia, a low shrub having the leaves covered with curious, scurfy hairs that give them a silvery appearance. The third family (Proteaceæ) has no familiar representatives.
The seventh order (Rosifloræ) includes many well-known plants, all of which may be united in one family (Rosaceæ), with several sub-families. The flowers are usually five-parted with from five to thirty stamens, and usually numerous, distinct carpels. In the apple and pear ([Fig. 114], I), however, the carpels are more or less grown together; and in the cherry, peach, etc., there is but a single carpel giving rise to a single-seeded stone-fruit (drupe) ([Fig. 114], E, H). In the strawberry ([Fig. 114], A), rose (G), cinquefoil (Potentilla), etc., there are numerous distinct, one-seeded carpels, and in Spiræa ([Fig. 114], F) there are five several-seeded carpels, forming as many dry pods when ripe. The so-called “berry” of the strawberry is really the much enlarged flower axis, or “receptacle,” in which the little one-seeded fruits are embedded, the latter being what are ordinarily called the seeds.