104 STABILIZATION AND CLIMAX. 



the two are necessarily very different in charactfer. Their one point in com- 

 mon is the position at the beginning of the course of development. As a 

 consequence, it is very convenient in analysis to use the term for the early 

 stages of either kind of sere, but always with the fact that it refers to position 

 and comparative characters clearly in mind. With more exact knowledge of 

 succession, and of the relation of the various secondary seres to the primary or 

 parental one, it will be possible to assign secondary initial stages to their 

 proper developmental position. 



The initial stages of primary seres are marked by extreme physical condi- 

 tions and by correspondingly specialized life-forms. Such primary areas as 

 open water, rock, dune-sand, etc., occur throughout the world. The life-forms 

 produced by them are likewise universal and, more interesting still, are highly 

 mobDe for the most part. Consequently, the pioneer aquatics of water areas, 

 the lichens and mosses of rocks, the xerophytic grasses of dunes, and the halo- 

 phytes of salt areas, consist of much the same species throughout the northern 

 hemisphere, and some of them occur in tropical and austral regions. Hence 

 the initial stages of water, rock, dime, or saline seres may be nearly or quite 

 identical in widely separated regions, with the result that the seres concerned 

 show increasing divergence to the various climaxes. From the extreme nature 

 of primary areas, and of the plants in them, initial stages persist for a long time, 

 largely because of the slowness of reaction and the incomplete occupation. 

 Primary areas differ much in these two respects. The greatest duration is 

 found in the initial stages of a took sere. The stages of a water sere follow 

 each other more rapidly, and those of a dune still more rapidly, though the 

 extent of the area in both cases plays a part (plate 28, a, b). 



The general limit of initial stages is indicated by a marked change ia the 

 extreme nature of the habitat and also by the degree of occupation in most 

 cases. Both of these are more or less closely associated with the accmnulation 

 of hirnius. In water the initial stagSs are best regarded as three or four, 

 ignoring the plankton. They are (1) the submerged stage, (2) the floating 

 stage, (3) the reed stage, (4) the sedge stage. It is obvious that any one or 

 more of these may be lacking, just as any one may be represented by a single 

 consocies, or even more imperfectly. In all of these the occupation is fairly 

 exclusive, and the reed and sedge communities are nearly or quite closed. The 

 initial conditions on rock vary greatly, and the initial stages are correspond- 

 ingly diverse. The longest series occurs on igneous rocks in dry or alpine 

 regions. The number of stages to a more or less closed community on a soil 

 with considerable hiunus is usually five: (1) crustose lichens, (2) foliose lichens, 

 (3) mosses, (4) cushion plants, (5) herbs and grasses. When the rock disin- 

 tegrates into sand or gravel the fourth stage often consists of bunch and mat 

 plants. In dunes and other primary areas, fans, deltas, etc., the number of 

 initial stages is often as few as one or two, though this depends much upon 

 water relations and the adjoining vegetation. In aU of these the earliest 

 stages of the water or rock sere are excluded, because the soil formation has 

 already taken place. A deposit in water, for example, may begin its develop- 

 ment at the floating, the reed, or the sedge stage, just as rock may disintegrate 

 without the presence of lichen or moss stages, and the succession begin with 

 the development of herbs or grasses. 



