REASONS FOR ORDER OF SUCCESSION 



457 



434. Reasons for order of succession. It is not always pos- 

 sible to explain in detail why each set of plants in a succession 

 takes possession of the ground and later on is itself driven out. 



FIG. 351. Young black oaks succeeding loblolly pine and shortleaf pine, 



southeastern Texas 



After von Schrenk 



In a general way it is clear that very low spore plants can 

 make a living on bare rock surfaces or on partly decomposed 

 rock where seed plants would find too little available salts, 

 especially nitrates, to support their nutrition. 



