Southeastern Washington and Adjacent Idaho. 101 



The Chara-Potamogeton Associes 



In shallow ponds and small clear streams it is not an unusual 

 sight to find the water rather completely filled with various sub- 

 merged plants, of which sometimes Chara and sometimes Pota- 

 mogeton pectinatus or P. calif ornicus are dominant. Perhaps 

 there occurs more often a mictium of the dominants of the two 

 consocies respectively. 



In addition to Vaucheria, Stigeoclonium, and other algae, which 

 are frequently very abundant in such situations, Najas flexilis, 

 Zannichellia palustris, and Batrachium aquatile, also help make 

 up the tangle of submerged plant life. 



The water crowfoot shows great plasticity in its habitat re- 

 quirements, and as the ponds become shallower it is not unusual 

 to find it dominating considerable areas of muddy banks. The 

 aerial leaves with their well developed blades appear in striking 

 contrast to the filiform submerged ones. 



- The role of these submerged plants in the preparation of a 

 suitable substratum for later stages in succession is frequently 

 very marked. As a result of the dense aggregation of the indi- 

 viduals of the constituent species of this community, bodies of 

 water often exhibit a pronounced accumulation of debris consist- 

 ing for the most part of the remains of former generations of 

 aquatic plants and animals but mixed ^ith fine soil particles 

 brought in by the action of wind and water, the whole being 

 effectively held in position by the expanding tangle of living 

 plants. The accumulation of humus decreases the total amount 

 of water in the substratum and the habitat gradually approaches 

 a little nearer the mesophytic. As the bottom of the pond is 

 slowly raised by the accumulating debris, the substratum be- 

 comes relatively more compact. 



A continuation of these processes reacts unfavorably upon the 

 submerged plants and they thus prepare the way for their own 

 elimination. Not only is the reaction of initial stages of succes- 

 sion unfavorable to the pioneer plant community but it also actually 

 favors invaders. Plants with slender stems and floating leaves, 

 such as Potamogeton and pond lilies, for a -time take possession 



101 



