354 



Aquatic .Societies 



The accompanying diagram 

 shows five modes of progress into 

 deeper water of pioneer land- 

 building plants. 



a is the method of the spike- 

 rush on gently sloping shore. It 

 is the method by which number- 

 less shore plants extend their hold- 

 ings, — subterranean off -shoots. 



b is the method of the tussock 

 sedges (see also fig. 209) which on 

 the loose mud in shallow waters 

 build up solid clumps. Many of 

 these, less than a foot in diameter, 

 are yet of such firmness that they 

 will sustain the weight of a man. 

 Every one knows such clumps, 

 from having used them (as step- 

 ping stones are used) in crossing 

 a swale. New offsets lie hard 

 against the old ones, roots descend 

 in close contact, and fibrous root- 

 lets interlace below in extraordin- 

 ary density. 



c is the method of the swamp 

 loosestrife, Decodon, a method of 

 advancing by long single strides. 

 The tips of the long over-arching 

 shoots dip into the water, and 

 then develop roots and buds and 

 a copious envelope of aerating tis- 

 sue. If these new roots succeed 



Fig. 211. Diagram illustrating the method of 

 advance into deeper waters of typical land- 

 building plants. 



a. Spike rush; b, tussock sedge; c, swamp 

 strife; d, cat-tail flag; e, Sphagnum and hea tti s 



loose- 



