288 PLANT PHYSIOLOGY AND ECOLOGY 



are known, their number and position often make it possible to 

 throw much Ught upon the previous course of development. In 

 the majority of cases the relict is not modified, and is readily 

 recognized as belonging properly to a previous stage. This is 

 true of herbs in all the stages of grassland and in the initial ones 

 of forest succession. The herbs and shrubs of the earlier stages, 

 which persist in the final forest formation, are necessarily modi- 

 fied. Their abundance and position, however, usually make it 

 clear that they are relicts. 



The lifetime of the forest and thicket stages of succession is 

 found by counting the annual rings of trees and shrubs. This 

 important method may be readily employed in woody formations 

 where stumps abound or a fire has occurred. 



Experiment 70. The study of a secondary succession. Select an 

 abandoned field or a denuded area for study. List the species that are 

 present, indicating their relative importance. Determine in so far as 

 possible the formations from which the invaders have come. Examine 

 similar areas, especially those that show other stages, and by means of 

 comparison indicate the general course of succession. 



Chart a permanent quadrat that has been previously established, 

 and compare the chart with those of former years. 



