ANOMALOUS SUCCESSIONS 121 



history is still a matter of conjecture. The original xero- 

 phytes are forced out not only by the disturbance of the 

 soil, but also by its increased water content. A few of them 

 often thrive under the new conditions, and, together with 

 the usual ruderal planes and a large number of lowland 

 mesophytes and amphibious forms derived from the banks 

 of the parent stream, constitute a heterogeneous association. 

 This is doubtless to be regarded as an initial stage of a suc- 

 cession, but it is an open question whether the succession 

 will early be stabilised as a new formation, or whether the 

 original vegetation will sooner or later be reestablished 

 under somewhat mesophytic conditions. Prom the number 

 of mesophytes and from the behavior of valleys, it seems 

 certain that the banks of such canals will ultimately be 

 occupied by a formation more mesophytic than hydrophytic, 

 into which some of the surrounding xerophytes of plastic 

 nature have been adopted. 



Anomalous successions are those in which the physical 

 change in the habitat is relatively slight, resulting in a dis- 

 placement of the ultimate stage, or the disturbance of the 

 asual sequence, merely, instead of the destruction and re- 

 construction of a formation, or the gradual development of 

 a new series of stages on new soil. In nature, the ultimate 

 grass or forest stage of a normal succession is often re- 

 placed by a similar formation, especially if the facies be few 

 or single. It is evident that certain trees naturally replace 

 others in the last stages of a forest succession, without 

 making the latter anomalous. The last occurs only when a 

 normal stage is replaced by one belonging properly to an 

 entirely different succession, as when a coniferous forest re- 

 places a deciduous one in a hardwood region. The presence 

 and development of such successions can be determined only 

 after the normal types are known. The interpolation of a 

 foreign stage in a natural succession, or a change of direc- 

 tion, by which a succession that is mesotropic again becomes 

 hydrophytic, is easily explained when it id the result of 

 artificial agents, as is often the case. In nature, anomalous 



