II.] 



ALISMACE^:. 



223 



water in Water Plantain : the sepaloid outer and peta- 

 loid inner perianth-leaves of Alisma : the stamens in three 

 series (9 altogether) in Flowering Rush (Butomus), and 

 the anomalous placentation of the same species ; the 

 numerous ovules not being confined to the ventral 

 sutures of the carpels, but scattered over the entire 

 walls. Arrowhead Sagittaria) differs from Alisma in 

 having the flowers unisexual and monoecious. 



65. Natttral Order Hydrocharideas. The Hydro- 

 char is Family. 



DISTRIBUTION. Another small cosmopolitan aquatic 

 Order. British genera 3, species 3. 



Floating or submerged Plants. Flowers unisexual. Ovary 

 syncarpous, inferior. 



Type Common Frogbit (Hydrocharis Morsus-rance). 

 Floating herb, with petiolate orbicular leaves, and 

 dioecious pedicellate flowers. 



OBSERVE the leaf-buds, about the size of small peas, 

 formed by the plant in autumn. These develop separate 

 plants in the following spring. Two or three buds thrown 

 into a pond have speedily covered it with Frog-bit. 



The "New Water-weed" {Elodea canadensis), an 

 American plant, was first remarked in Britain in 1817, 

 but was a rare plant prior to 1848, since about which 

 time it has become distributed with marvellous rapidity 

 in the rivers, canals and ponds of the midland counties. 



