486 D1COTYLEDONES. 



bium, Circcea are natives of this country ; Trapa is extinct in this country, it 

 has been found in a semi-fossilized condition near Cromer and in bogs in Den- 

 mark, and existed in Sweden until a few years ago ; (Enothera has been intro- 

 duced from N. Am. A number of N. Am. species are grown as ornamental 

 plants in our gardens. The seeds of Trapa natans are edible, and used as food 

 in China. 



Order 5. Haloragidacese. This is a reduced form of the 

 CEnotheracese, and principally differs from these in the presence of 

 endosperm and/ree styles. Only 1 ovule in each loculus. 84 species 

 distributed over the entire globe ; the majority are aquatic plants. 

 The most advanced type is Myriophyllum (Water-Milfoil), with a 

 regular, epigynous flower (S4, P4, A4 + 4, G4), most frequently 

 diclinous (monoecious) ; the fruit is a Z-^-partite schizocarp. 

 Aquatic plants, most frequently with pectinate, pinnate leaves. , 

 Haloragis. Gunnera (a dozen species from the Southern Hemisphere) forms 

 the next step in the reduction. Large, scattered, rough-haired, and softly- 

 spined leaves, with small flowers in crowded inflorescences. The flower, when 

 most complete, has S2, P2, A2 (petal-stamens) and G2, forming an inferior, 

 unilocular ovary with 1 ovule. It is remarkable for the great number of 

 stipules placed in transverse rows in the leaf-axils, for the peculiar glandular 

 organs, and for the colonies of Nostoc, which are found embedded in the 

 cortex as a kind of parasite. The simplest form is Hippuris (Mare's- 

 tail) with an extremely small, crenate or entire calyx, without 

 corolla, and with only one stamen and one carpel, forming an 

 inferior, unilocular ovary with only one ovule. Fruit a drupe 

 with thin pulp. It is an aquatic plant with creeping, sympodial rhizome, 

 and erect unbrancned shoots, bearing numerous small, verticillate leaves. The 

 small flowers are situated singly in the leaf-axils. 



Order 6. Rhizophoraceae. Tropical trees or shrubs (50 species, the best 

 known being Hhizophora mangle, Mangrove) which grow gregariously, especi- 

 ally along the banks of rivers and by sea-coasts, where the water is quiet and 

 brackish, and where they form the so-called Mangrove-swamps. Aerial roots 

 .are formed on the stems and branches (Fig. 522 A). The seeds germinate in 

 the fruit, which by arrest contains only one seed (Fig. 522 B), before it is 

 detached from the tree. The radicle projects considerably from the seed, and 

 hangs down freely in the air ; when the embryo is finally detached from the 

 mother-plant, the separation is effected by the hood-like cotyledon, which 

 entirely envelops the plumule, becoming detached from tbe rest of the embryo, 

 which falls down, while the hood-like cotyledon remains enclosed in the fruit. 

 The embryo, after it has fallen, strikes root, and continues growing in the 

 undisturbed mud under the trees, or perhaps it may first be drifted about by 

 the water, being well adapted for this by its peculiar, tough nature, and large, 

 intercellular spaces. It may also further be remarked that the anther is divided 

 iuto a number of small locnli. The leaves are stipu'ate. The endosperm projects 

 from the micropyle, growing out from the base of the seed, and thus serves as 

 an organ of suction to convey nutriment to the embryo from the mother-plant. 



