The third order of the Eucyclæ, the Æsculinæ, embraces six families, of which three, the horsechestnuts, etc. (Sapindaceæ), the maples (Aceraceæ), and the milkworts (Polygalaceæ), have several representatives in the northern United States. Of the first the buckeye (Æsculus) ([Fig. 108], J) and the bladder-nut (Staphylea) ([Fig. 108], G) are the commonest native genera, while the horsechestnut (Æsculus hippocastanum) is everywhere planted.
The various species of maple (Acer) are familiar examples of the Aceraceæ (see [Fig. 106], A, F).
The fourth and last order of the Eucyclæ, the Frangulinæ, is composed mainly of plants with inconspicuous flowers, the stamens as many as the petals. Not infrequently they are diœcious, or in some, like the grape, some of the flowers may be unisexual while others are hermaphrodite (i.e. have both stamens and pistil). Among the commoner plants of the order may be mentioned the spindle-tree, or burning-bush, as it is sometimes called (Euonymus) ([Fig. 109], A), and the climbing bitter-sweet (Celastrus) ([Fig. 109], D), belonging to the family Celastraceæ; the holly and black alder, species of Ilex, are examples of the family Aquifoliaceæ; the various species of grape (Vitis), the Virginia creeper (Ampelopsis quinquefolia), and one or two other cultivated species of the latter, represent the vine family (Vitaceæ or Ampelidæ), and the buckthorn (Rhamnus) is the type of the Rhamnaceæ.
Fig. 109.—Eucylæ (Frangulinæ), Tricoccæ. A, flowers of spindle-tree, Euonymus, (Celastraceæ), × 1. B, cross-section of the ovary, × 2. C, diagram of the flower. D, leaf and fruit of bitter-sweet (Celastrus), × ½. E, fruit opening and disclosing the seeds. F, section of a nearly ripe fruit, showing the seeds surrounded by the scarlet integument (aril). em. the embryo, × 1. G, flower of grape-vine, Vitis (Vitaceæ), × 2. The corolla has fallen off. H, vertical section of the pistil, × 2. I, nearly ripe fruits of the frost-grape, × 1. J, cross-section of young fruit, × 2. K, a spurge, Euphorbia (Euphorbiaceæ), × ½. L, single group of flowers, surrounded by the corolla-like involucre, × 3. M, section of the same, ♂, male flowers; ♀, female flowers. N, a single male flower, × 5. O, cross-section of ovary, × 6. P, a seed, × 2. Q, longitudinal section of the seed, × 3. em. embryo.
The fifth group of the Choripetalæ is a small one, comprising but a single order (Tricoccæ). The flowers are small and inconspicuous, though sometimes, as in some Euphorbias and the showy Poinsettia of the greenhouses, the leaves or bracts surrounding the inflorescence are conspicuously colored, giving the whole the appearance of a large, showy, single flower. In northern countries the plants are mostly small weeds, of which the various spurges or Euphorbias are the most familiar. These plants ([Fig. 109], K) have the small flowers surrounded by a cup-shaped involucre (L, M) so that the whole inflorescence looks like a single flower. In the spurges, as in the other members of the order, the flowers are very simple, being often reduced to a single stamen or pistil ([Fig. 109], M, N). The plants generally abound in a milky juice which is often poisonous. This juice in a number of tropical genera is the source of India-rubber. Some genera like the castor-bean (Ricinus) and Croton are cultivated for their large, showy leaves.
The water starworts (Callitriche), not uncommon in stagnant water, represent the family Callitrichaceæ, and the box (Buxus) is the type of the Buxaceæ.
