208 



PLANT PHYSIOLOGY AND ECOLOGY 



aspects, however, the rule is to indicate only the characteristic 

 species, i.e., those that flower at the time concerned. The legend 

 giving the list of abbreviations and species is placed directly 

 below the chart. Each chart is numbered, and the formation, 

 place, and date indicated. When physical factors are deter- 

 mined for the quadrat, these are recorded upon the chart in so 

 far as possible. 



223. The permanent quadrat. Chart quadrats which are 

 marked so that they can be visited and studied from year to year 

 are permanent quadrats. The latter are indispensable for follow- 



^ 



.** * ^ 









Fig. 75. A permanent and a denuded quadrat in the gravel slide forma- 

 tion. Both quadrats were charted and one then denuded. 



ing the changes of aspects with the season and the slow yearl}^ 

 changes which formations undergo in their development. Since 

 they record the existing structure as well as its subsequent changes, 

 permanent quadrats are used almost exclusively in preference to 

 list and chart quadrats. Practically all formations are constantly 

 undergoing more or less change, much of which is so slow or obscure 

 that it can be discovered only by the permanent quadrat. New 

 plants are entering through invasion, others are disappearing in 

 consequence of it. The extent and rapidity of such changes can 

 be ascertained only by the minute and repeated study of a definite 

 area. This is especially true where one formation is being replaced 



