22 UTEICULAKIA. [CLASS H. ORDER i. 



Sloy, and " in many parts of Scotland, extending its range even to 

 Skye" (Hook) 



Perennial ; flowering June and July. 



The plants in this genus are extremely interesting, from the crested 

 vesicular, or bladder -like, bodies that are developed on their immersed 

 stems, leaves, and even roots. During certain seasons of the year the 

 whole plant is submerged, and if the vesicles are then examined (as was 

 remarked by Hayne) they will be found filled with water; but as the 

 season advances, and the flowers begin to be developed, it is necessary 

 they should be elevated above the surface of the water. To accom- 

 plish this, the little bladders, which have an opening closed by an 

 elastic valve, are now found to contain air in place of the water, by 

 which means the whole plant is buoyed up and rises to the surface ; 

 the flowers then expand themselves, and perform the functions neces- 

 sary for the fertilization of the ovules, and the seeds are ripened ; after 

 which the air again gives place to water, the whole plant sinks to the 

 bottom, and carries with it its seed, thus depositing it in the situation 

 and soil most fitted for its propagation. The means by which the water 

 is displaced in the vesicles and filled with air, is not satisfactorily known. 

 It " is probably separated by the vital agency of the vegetable, and 

 during its gradual evolution the water is expelled, and is prevented 

 returning either by the mechanical structure of the valve, or by the 

 constant evolution of air" (Burnett). 



Few instances in the economy of vegetation more forcibly arrest 

 the attention, than the beautiful contrivance displayed iu this curious 

 genus of aquatic plants. They are found both in hot, and in cold 

 countries, but far more abundant in the former than the latter. In 

 Great Britain, their natural habitats are for the most part in stag- 

 nant pools, lakes, and clear water frequently attached to the bottom, 

 several feet below the surface ; in such situations they remain securely 

 protected from the severity of winter, through the medium of the 

 scarcely varying temperature of the element by which they are sur- 

 rounded. There are many other admirable contrivances of nature 

 which equally illustrate the unerring means by which PROVIDENCE 

 accomplishes his designs in the vast field of vegetable creation. We 

 may here mention the beautiful aquatic, Pontedcria crassipes, in- 

 troduced into this country from Guiana in 1825. This, although 

 a water plant, will flourish for a considerable time in a pot of 

 light earth ; and when grown in this way, the leaves are large, with 

 fleshy stalks of equal thickness throughout: but if the plant is placed 

 in water, the leaf-stalks become inflated with air, frequently assuming 

 an orbicular form, and equal in diameter to the leaf itself. If the 

 plant be again elevated above the water, the roots still remaining 

 within it, the air will be expelled, and the stalks resume their former 

 appearance. 



