60 G. D. FULLER AND A. L. BAKKE 



best. It cannot be directly compared with frequency percent 

 which is determined by means of various different sample plot 

 and is a proportional relationship, while areal percent is an abso- 

 lute determination. Here again it seems that -samples of 0.1 

 sq. m. are preferable because it is desirable to determine frequency 

 at the same time as extent of distribution. 



13. Areal percent determinations include all species having 

 living aerial organs inside the boundary whether they are rooted 

 or have perennial shoots. If this is compared with the rules 

 for frequency determination, it will be seen that the frequency 

 percent determined from a number of plots in which the species 

 really occurs does not necessarily coincide with the species' actual 

 frequency percent and should therefore be represented in another 

 way; e.g., AF% (Areal frequency). 



14. Areal percent is obtained by estimating the number of 

 surface units covered within the limits of a single sample plot; 

 for example 10: here the sample is jknown to be divided into 10 

 equal parts and these are examined in turn for the number of 

 units covered by the given species. The sum of the observed 

 areas covered gives the areal percent. 



15. The samples are located and marked out with the assist- 

 ance of the same apparatus that is used in the frequency deter- 

 minations. This may be accomplished by using a ring upon a 

 walking stick with two radial rods that mark off a sector (of the 

 circular sample) of a size which gives the smallest distributional 

 unit area we wish to examine. 



16. In the usual study of a formation, the areal percent will 

 be of no great significance because its value in interpreting the 

 physiognomy is too small a return for the labor required and we 

 must remain content with a descriptive analysis of the contri- 

 bution to the physiognomy made by a species' frequency. When, 

 however, in a definitely limited area the small yearly variations 

 in the abundance of a species are to be compared, the areal 

 percent calculations will be very significant. 



