LAND-FORMING PLANTS. 69 



against the scour of the tide. Cochkaria has a remarkably neat 

 way of protecting its young leaves. The young leaf is doubled 

 and placed round the stalk of the next oldest. At the tip of the 

 leaf is a little white scar which entirely protects the leaf below. 



On the opposite side of the Clyde above Dumbarton Rock, 

 Scirpus maritimus acts in a very similar way. The annual advance, 

 probably 4 inches, is, however, not so great. There is, in this 

 case, a peculiar little tuber formed at the end of each rhizome. 

 It is carefully protected, first by the bases of the old leaves which 

 wither on it, and secondly, by ihe pericycle becoming a hard 

 sclerenchymatous shell. Thus it is very well suited to resist small 

 animals, and even when uprooted and washed to and fro in the 

 tide, it does not break off. 



Scirpus (Blysmus) rufus, which is to be found on the Langbank 

 side, has the simple typical growth of a sympodial rhizome, yearly 

 pressing some 2 or 3 inches seawards. It is therefore a land- 

 former, though by no means of the same importance as Scirpus 

 lacustris. 



The entire genera of Scirpus and Carex have a general ten- 

 dency to this creeping rhizome habit. In the water-forms and 

 Carex arenaria the rhizome is very long, and in those of dry land 

 it tends to shorten so as to form a tuft or bunch of stems. I think 

 that in the water species the untidy remains of dead stems are 

 really of great importance to the plant. The leaves being strictly 

 sheathing and more or less triangular in shape admit of an air- 

 passage between them, and down this, no doubt, travels the oxygen 

 required by the mud-buried rhizomes. In most also the dead 

 leaves, or their bases at least, are never thrown off, but remain as 

 a sheath which is burst through by the developing roots and 

 rhizomes. It is probable that most of the valuable organic matter 

 of the leaf is thus never lost, but passes into the rhizomes. 



Amongst fresh water land-formers of a similar type Phragmites 

 communis is very conspicuous — for example at Possil Marsh. Its 

 rhizomes are at times 16 feet in length, and from them are given 

 off sideways much shorter branches ; the arrangement in some 

 cases being almost like the ribs and keel of a ship, though apt to 

 be irregular. This plant covers many square miles in the Danube 

 region, as well as in the Caspian, and in Australia. It is said to 

 reach a height of 18 feet, and can grow in 9 feet of water. 



