I 86 PLANT LIFE. 



(7) open water which, however, is full of floating 

 Diatoms {Plankton), and under which there may be a 

 sort of subaqueous meadow of the Alga, Chara, which 

 is in France found to a depth of 36 feet. A similar 

 general succession of Wet Meadow plants, Eush, Flag, 

 Reeds, Water-lily, Pondweed and Plankton seems very 

 common throughout Northern Europe.^ 



In each of these belts it is easy to note some of the 

 more obvious adaptations of the plants to their par- 

 ticular position in the water. The whole series, from 

 the Rushes downwards, including the Water-lily and 

 Potamogeton, have a very characteristic texture. They 

 contain many air cavities which fulfil a double function : 

 the oxygen required by the living cells for respiration 

 or breathing is difficult to obtain in the case of water- 

 plants, and so air fills the hollow spaces. The presence 

 of the air-chambers also makes the plant buoyant and 

 able to float freely. There are other easily distinguished 

 characters of the water-flora, such as very little woody 

 tissue or cork, and often no stomata. 



The Reeds vary considerably, according to the slope 

 of the pond or loch Where it is very steep, such 

 forms as Equisetum limosum occur. If it is gradual, 

 Phragmites communis is generally the most conspicuous 

 form. This plant has extremel)^ long runners, which 

 may grow out towards the water for a length of i 6 feet. 

 From the main submerged stem a series of branches are 

 given off at close intervals, and these latter curve 

 upwards, and develop their leaves above the water. In 

 some parts of the Danube valley, this plant covers an 



^ Warming describes an almost identical series in Scandinavia. In the 

 Jura the order has been given (Magnin) as follows : (2) Sedges ; (3) Phrag- 

 mites, that is, the Reed grass (see below) ; (4) Scirpus ; (5) Yellow Water- 

 lily (9-15 feet depth water); (6) Potamogetons (12-24 feet); (7) Chara 

 (24-36 feet). 



