CLASSIFICATION OF THE MONOCOTYLEDONS. 167 



roots (Corallorhiza) , of which there are several species, are 

 examples of these, and another closely related form, the putty- 

 root (Aplectrum) (Fig. 90, A), has the flowering stems like 

 those of Corallorhiza, but there is a single, large, plaited leaf 

 sent up later. 



ORDER VII. Helobice. 



The last order of the monocotyledons is composed of marsh 

 or water plants, some of which recall certain of the dicotyledons. 

 Of the three families, the first, Juncaginece, includes a few in- 

 conspicuous plants with grass-like or rush-like leaves, and small, 

 greenish or yellowish flowers (e.g. arrow-grass, Triglochin). 



The second family (Alismacece) contains several large and 

 showy species, inhabitants of marshes. Of these the water- 

 plantain (Alisma), a plant with long-stalked, oval, ribbed 

 leaves, and a muth-branched panicle of small, white flowers, 

 is very common in marshes and ditches, and the various 

 species of arrowhead (Sagittaria) are among the most charac- 

 teristic of our marsh plants. The flowers are unisexual ; the 

 female flowers are usually borne at the base of the inflores- 

 cence, and the male flowers above. The gynoecium (Fig. 91, JB) 

 consists of numerous, separate carpels attached to a globular 

 receptacle. The sepals are green and much smaller than the 

 white petals. The leaves (F) are broad, and, besides the 

 thickened, parallel veins, have numerous smaller ones connect- 

 ing these. 



The last family is the Hydrocharidece. They are submersed 

 aquatics, or a few of them with long-stalked, floating leaves. 

 Two forms, the ditch-moss (Elodea) (Fig. 91, G, I) and eel- 

 grass (Vallisneria) are very common in stagnant or slow- 

 running water. In both of these the plants are completely 

 submersed, but there is a special arrangement for bringing 

 the flowers to the surface of the water. Like the arrowhead, 

 the flowers are unisexual, but borne on different plants. The 

 female flowers (H, L) are comparatively large, especially 



