510 VALLISNERIA ORDER ALISMACEJE. 



very curious contrivance. They are themselves so constructed 

 as to be lighter than water, and they are mounted on long cork- 

 screw-like stalks, which are endowed with elasticity enough to 

 enable them to extend when the surface of the water rises, just 

 like a spiral spring when it is stretched out ; whilst these con- 

 tract again as the water sinks, so as still to keep the flower in 

 close apposition with the plant. But the staminiferous flowers 

 have no such provision ; and as these grow from the part of the 

 plant which is continually submerged, it would not seem evident 

 how they are to come into proximity with the others, more 

 especially as they commonly grow from separate roots. It has 

 been observed, however, that, when the pollen is mature, and 

 the anthers are ready to burst, the flowers producing it detach 

 themselves ; and, rising by their lightness to the surface of the 

 water, they mingle with those already floating there, and dis- 

 charge upon them their pollen, as soon as their petals are ex- 

 panded under the influence of the sun. It has been further 

 observed that, when the seeds are ripened, the spiral peduncle 

 again contracts ; and, carrying down the capsule, buries it in 

 the mud. 



687. The plants of this order are found in the ponds and 

 streams of most countries ; scarcely any of them, however, have 

 been applied to any useful purpose ; and none are characterised 

 by any remarkable properties. 



688. Another small order of 

 aquatic Endogens is the one to which 

 the Sagittaria (. 227) belongs ; it 

 also includes a still more common 

 plant, the Alisma Plantago, or 

 Water Plantain, from which the 

 name of the order, ALISMACE^J, is 

 derived. These are alike in most 



, i , Fro. 183. FLOWER OP ALISMA 



respects, in the Structure 01 the PLANTAGO, with the corolla removed, 



parts of fructification : but the 8bowin s three se pais of calyx, and 



six stamens; a, undeveloped stamen. 



former has the pistillme and stami- 

 niferous flowers distinct (hence belonging to the Linnsean class 



