ALISMACEJ!;. 495 



all similar, or 3 outer small and sepal-like, and 3 inner ones 

 larger and petal-like. Stamens 6, 9, or indeiinite. Ovary of 

 8, 6, or many carpels, either distinct from the first or separable 

 when in ripe fruit, each with 2 or many ovules. Seeds con- 

 sisting, within the testa, of a homogeneous mass, usually con- 

 sidered as an undivided embryo without albumen. 



The genera are not numerous, but several of them dispersed over the 

 greater part of the vrorld. 



Perianth-segmenta all nearly equal, large and coloured. Flower- 

 stem tall, with a large terminal umbel 1. BuTOMB. 



Perianth-segments 3 small and herbaceous, 3 large and coloured. 

 Flowers opposite or whorled, in a terminal raceme, umbel, or 

 panicle. 



Carpels and stamens numerous. Leaves sagittate 2. ABROWHEAr. 



Carpels numerous. Stamens 6. Leaves ovate or narrow ... 3. Alisma. 



Carpels 6. Stamens 6. Leaves ovate or oblong 4. Damasonium. 



Perianth-segments all small and shghtly coloured. Flowers alter- 

 nate, in a raceme or spike. 



Carpels 3, distinct. Stem leafy, rush-like 5. Scheuchzekia. 



Carpels 3, united till they ripen. Leaves linear, all radical ... 6. Tkiqlochiit. 



I. BXrrOME. BUTOMUS. 



A shigle species, distinguished from Alisma as a genus, or by some bo- 

 tanists as an independent family, chiefly on account of the ovary, vrhich has 

 several ovules in each carpel. 



1. Common Butome. Butomus umbellatus^ Linn. 

 (Eng. Bot. t. 651. Flowering Rush.) 



A perennial, with a thick, creeping rootstock, and long, erect, sedge-like 

 triangular radical leaves, broad and sheathing at the base. Flower-stem 

 leafless, 2 to 4 feet high, thick and rush-like, bearing a large umbel of showy, 

 rose-coloured flowers, with 3 lanceolate, thin bracts at its base. Pedicels 3 

 to 4 inches long, often 20 to 30 in the umbel. Perianth full an inch dia- 

 meter, cff 6 ovate, spreading, nearly equal segments. Stamens 9. Carpels 6, 

 erect, tapering into short styles, each with numerous minute seeds. 



In watery ditches, and still waters, over the greater part of Eui'ope and 

 Eussian Asia, except the extreme north. Dispersed over central and south- 

 ern England and Ireland, but believed to be introduced only into northern 

 England and southern Scotland. Fl. stimmer. 



II. ARRO'WHSAD. SAGITTAEIA. 



Aquatic herbs, differing from Alisma in their unisexual flowers, the males 

 with numerous stamens, the females with very numerous small carpels in a 

 dense head. 



Besides the common species, there are several from North and South 

 America, and eastern Asia. 



1. Common Arrowhead. Sagittaria sagittifolia, Linn. 

 (Eng. Bot. t. 84.) 

 A perennial, with a creeping rootstock, forming bulb-like tubers. Leaves 

 radical, rising out of the water on very long stalks ; the blade 6 to 8 inches 



