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HI.] HYDROCHARIDEM. 



Type — Hydrilla verticillata. 



A submerged water-plant, with small, verticillate leaves 

 and axillary, unisexual flowers. 



Observe the male flowers, which break off from the 

 plant at the time of expansion, and float to the surface in 

 order to fertilise the females, as in Vallisneria, another 

 genus of the Family, occurring both in India and Europe. 

 In Vallisneria the female flower is borne upon a long, 

 spirally-twisted peduncle, which permits it to reach the 

 surface while still attached. 



The Type-species is one of the common water-plants 

 used by sugar-refiners in claying sugar. The moisture 

 which it contains slowly percolates the sugar, carrying off 

 impurities, which are deposited in the clay. It closely 

 resembles a species {Elodea canadejisis) which has of late 

 years been imported from America into England and 

 Europe, where it has multiplied so rapidly as to obstruct 

 navigation in still-flowing rivers and canals. 



Ottelia alismoides, with radical, petiolate, ovate leaves, 

 is common in India. 



The submerged leaves of several species of this Family 

 are well suited to show the rotation of the cell-sap in their 

 individual cells. To observe it, place thin, longitudinal 

 sections, or the membranous margin of a leaf, under a high 

 magnifying power. 



