258 



ANNUAL, REPORT SMITHSONIAN INSTITUTION, 1020. 



glance. Three illustrations from the paper cited may be reproduced 

 here. 



5+ 



4 



3 



2 



1 



This represents Clelhra alnifolia, the "optimum acidity" 

 for which is plainly shown to be specific acidity 300+ , 

 and the "range" rather limited, at most from acidity 

 300+ to 30+. 



This represents Pyrola amerkana, the optimum acidity for 

 which is shown to be specific acidity 30+ and the range 

 rather wide, from specific acidity 300+ down to 3+. 



This represents Rhododendron maximum, for which the range 

 is from the greatest acidity met with in normal soils down 

 to the neutral point; and the optimum is apparently at 

 specific acidity 30+ . 



For comparison of a large number of species, it is simpler to indi- 

 cate the frequency of observations of each degree of acidity by the 

 use of different type, lower case x signifying rarely observed, 

 capital X frequently observed, and bold face X the optimum or most 

 frequently observed value. The three illustrations just given would 

 appear under this plan as follows : 



The latter plan is used throughout the present article. 



Explanation of Table 6. — In the table as originally published the 

 plants were arranged in the order adapted to bring out their botanical 

 relationship. Here they are divided into three groups on that basis, 

 but in each group (or subgroup in the case of No. 3) the species are 

 listed in the order of diminishing alkalinity and increasing acidity 

 of their soils. 



