I 88 PLANT LIFE. 



area of many square miles, and grows, in some cases, to 

 a height of i8 feet. In the Clyde valley it is often 

 1 3 feet high. It is clear that these submerged 

 horizontal stems and branches will enable the Reed- 

 association to grow out into the pond. An arrangement 

 of this kind is very necessary, on account of the way in 

 which the water becomes filled up near the edge of the 

 pond in the zones of the Iris and Rush. 



In these, the tangle of plants is so great, that it is 

 difficult at first to make out any distinct system ; but 

 close observation shows, that almost all the plants 

 have something of the same way of growth as 

 the Phragmites. The main stems grow horizontally, 

 and the branches vertically. The former are either 

 lying on the mud, like the Iris or Marestail, or perhaps 

 floating submerged in the water, as in the cases of the 

 Bogbean {Menyantkes trifoliatd), and the tough horizontal 

 stems, sometimes three feet long, of the Marsh Cinquefoil 

 {Comarum palnstre). The net result is a series of 

 horizontal stems at different depths, and from these a 

 sort of forest of upright branches, of which some carry, 

 like Hippuris, submerged leaves, and others, like the 

 Iris, hold their foliage entirely out of the water. 



The Comarum leaves are generally in the air; but they 

 are liable to be accidentally plunged below the water, and 

 so they are specially protected against this danger. If a 

 leaf is dipped in water, it will be covered by a beautiful 

 silvery lustre (an air film), and, on withdrawal, it is found 

 to be perfectly dry. There is a development of wax 

 upon the leaf which prevents its being permanently 

 wetted. 



A clear idea of the forces at work in the tangle of 

 plants near the margin, can only be obtained by the 

 use of the imagination, supplemented and corrected by 



