246 



HINTS AND NOTES 



abundant. Diatoms, which require water with 

 a good deal of mineral salts (alkaline), are 

 found in more lowland situations. 



Flowering plants are equally susceptible to 

 differences in the water. The Stoneworts or 

 Charas luxuriate in water highly charged with 

 carbonate of lime, and help to precipitate it, 

 as do some mosses. 



Water may also vary in temperature, but in 

 the British Isles there is little variation in this 

 respect. Sea-water, however, is more constant 

 in temperature than other waters, and is seldom 

 frozen. The water of lowland ponds and lakes 

 is not so readily frozen as that of highland 

 lakes, &c. The depth of the water naturally 

 influences the temperature, hence the zonal 

 arrangements of plants, which are connected 

 with the individual thermal constant. 



The state of motion of the water again is 

 important. When motionless it may be actually 

 foul, or merely stagnant, and in the first case 

 few flowering plants will live in it. But some 

 plants require stagnant, motionless water, as 

 Bladderwort. Naturally such waters are rela- 

 tively rich in mineral salts, and so are those 

 that move but slowly, in which the pondweeds 

 luxuriate. The quickly-moving waters are far 

 less rich in salts, and so are the upland lakes 

 and tarns. 



Much depends upon whether water is of 

 aerial origin, or telluric, or underground. The 

 aquatic element, beneficial as it is in many re- 

 spects, however renders transpiration difficult, 

 and the supply of oxygen is small except in 

 running water; hence the distinctions between 

 aquatic associations due to the aerating power 

 of water. 



Then, again, light is impeded, and no light 

 penetrates at the greater depths. The char- 

 acter of the light is also different, for red and 

 yellow rays are absorbed, and the light alters 

 from white at the surface to a green colour 

 below, hence the apparent colour of clear water 

 is green, or, as in the case of the still deeper 

 sea, blue. Hence the colour types of marine 

 algae, red, brown, and green, the green colour 

 in the first two being masked by colouring 

 matter, anthocyan, &c. 



Altitude of Aquatic Vegetation. There are 

 distinct zones of altitude of the different types 

 of aquatic vegetation. The maritime vegeta- 

 tion or marine plants grow at sea-level. It is 

 important to remember that inland water finds 

 its own level and flows, unless enclosed as in 

 a pond, lake, loch, lough, or tarn, regularly by 

 a series of stages to the sea from the highest 

 points to lower levels. 



This gives a division into highland and low- 

 land aquatic vegetation. In the highland loch 

 are found such plants as Awlwort, Alternate- 



flowered Water Milfoil, Starwort, Lobelia, 

 Bladderwort, Shoreweed, various types of 

 Pondweeds, Spike Rush, Floating Bulrush, 

 Pillwort, &c., and White Water Lily, Float- 

 ing Marshwort, Amphibious Knot Grass, and 

 other Pondweeds are floating types ; whilst in 

 the Reed swamp grow Bog Bean, Floating Bur 

 Reed, Common Spike Rush, Bulrush, Prickly 

 Twig Rush, Sedges, Reed, Manna Grass, &c. 



There are the upland quickly-flowing rivers, 

 which again are poor as a rule in mineral 

 salts, further differentiated by relative altitude. 

 The lowland rivers are more or less stagnant 

 or slow-flowing, and are richer in mineral 

 salts. They form in the first case tracts like 

 the Norfolk broads, very little above sea-level. 

 The slow-flowing rivers are intermediate in 

 altitude, and their vegetation differs from the 

 last, being much richer in the forms of plant 

 life. 



Transition of Aquatic to Marsh or Bog Vege- 

 tation. Aquatic vegetation is distinguished by 

 the immersion of the plants entirely, or nearly 

 so, in water. The land vegetation forms the 

 opposite extreme, for water there, except in 

 low-lying areas, does not lie near the surface 

 except on clay soils. Thus the relative lie of 

 the ground, and the porous or non-porous 

 character of the soil, determines largely the 

 gradation from a dry to a wet meadow. Be- 

 tween these two types aquatic and land plants 

 lies an intermediate series, the Hygrophiles 

 or marsh plants and wet meadow types, into 

 which the former may merge. 



Thus an aquatic formation may, through 

 the marginal reed swamp, become a marsh 

 formation laterally ; the latter may also, where 

 peat is formed to a considerable depth, and the 

 lime salts are gradually lost, become a bog or 

 fen. The aquatic and fen or bog formations 

 on a large scale are largely transitional in 

 East Anglia, and the preference of each for 

 alkaline water renders such transitions easy. 

 Highland bogs, however, are poor in lime 

 and richer in humous acids. 



Drainage and Aquatic Vegetation. Tem- 

 porarily a dry season or drought, especially in 

 the case of pools or ponds, has a great effect 

 upon the vegetation. Pools may dry up, as 

 they have done almost everywhere, and a relic 

 of a bog flora, with Sundew or Butterwort, 

 disappear for ever. The felling of trees may 

 artificially cause desiccation over a wide area, 

 and conduce to the disappearance of marsh 

 or aquatic plants in much the same way; 

 whilst on the contrary, the destruction of a 

 forest naturally and the water-logging of the 

 area may give rise, as has occurred over and 

 over again in upland areas, to a bog. But 

 by far the most potent factor in disturbing the 



