ingless. After we discovered that pH and water temperature often varied at 

 minute distances, both laterally and vertically, this time-consuming routine was 

 discontinued. 



II. Peculiarities and Distribution of Aquatic and Wetland Vascu- 

 lar Plants 



Aquatic plants are paradoxical in that while many are of ^<reat economic import 

 in relation to the existence, reproduction and conservation of wild life they may 

 simultaneously be a hindrance and detriment to man's hydrological activities such 

 as those involving navigation and irrigation. 



The establishment and existence of wetland plants in their particular habitat 

 is much less complicated than that for strictly aquatic plants. To exist under 

 water, vascular plants must have sufficient light and critical gases to carry on 

 photosynthesis. The depth at which they grow depends largely upon the intensity 

 and spectral composition of light. This becomes especially critical in waters that 

 are variously polluted. Sedimentation created by floods and erosion, and turbidity 

 as a result of dissolved organic matter and suspended organic and inorganic parti- 

 cles, may cloud and discolor the water and reduce to a bare minimum the possi- 

 bility of a plant carrying on the photosynthetic process. 



As has been noted by other researchers, individuals of some species grow under 

 a single set of environmental conditions, while the individuals of other species 

 will occur under the selective regime of different sets of environmental conditions. 

 These latter species exhibit a wide degree of tolerance, such as cat-tails (Typha), 

 ZannichelUa, Najas, and Riippia, usually found in fresh-water situations but that 

 also can tolerate saline and alkaline conditions. The quality of water often, but 

 not always, determines the plant community that will be developed in the environs. 

 There is little question, however, that salinity has a critical and intricate influence 

 upon the composition and development of maritime and littoral ecosystems. 



While various physical and chemical factors of the aquatic environment have 

 a definite influence upon the life activities of vascular hydrophytes, the converse 

 is also true as has been succinctly stated by Sculthorpe (1967. p. 415). 



"As a result of the relatively restricted volume of any inhabited body of water, 

 aquatic vegetation exserts a much more profound influence upon its environment 

 than does terrestrial vegetation. Through their photosynthesis and respiration, and 

 their manner and rate of growth,, vascular hydrophytes may have very significant 

 efi'ects upon such environmental factors as the concentrations of dissolved oxygen, 

 carbon dioxide and ammonia, mineral nutrient supplies, pH value, light penetra- 

 tion, current velocity and rate of silting. These effects can wield a direct or in- 

 direct influence on the lives of other aquatic organisms, notably the microflora 

 and fauna for which the hydrophytes may provide support, shelter or food. The 

 impact of hydrophytes on the environment and on biotic relationships increases 

 as the volume of the water-body diminishes; plants are most significant in ponds, 

 canals and stagnant swamps, and in most rivers, which arc usually shallow com- 

 pared to lakes and so contain a relatively greater concentration of plants. Analysis 

 of these ecological interactions presents a formidable problem: the tremendous 

 variation in local edaphic and biotic conditions invalidates all but a very few 

 generalisations." 



The ecosystems of aquatic and wetland habitats, though not at all consistent 

 as to their floral content, are made up of characteristic ecotypes for each kind 

 of system. In other words, the species composition of a given ecosystem may vary 

 in accordance to its geographical location but each kind of habitat usually has its 

 characteristic type of flora. 



