96 PROCEEDINGS OF THE ACADEMY OF [Mai'ch, 



Many tests made in this region are included in the tables for indivi- 

 dual ericaceous species which follow. 



Observations on Individual Species 



In order to bring out the acidity relations of the individual species, 

 the plan suggested in the paper above cited* has been modified 

 in such a manner that while the specific acidities are plotted hori- 

 zontally the number of places where each value has been observed 

 are now plotted vertically. Thus, on p. 97, when a given species 

 has been found to grow in a soil with specific acidity = 100 at two 

 different localities (or distinctly different habitats in the same 

 locality) an x is placed above the figure 100 and opposite the number 

 2. Observations in nurseries are marked with n, and those made 

 in other regions, which seem worth introducing for comparison, 

 with 0. A curve may be regarded as drawn through the points thus 

 marked, and from its shape the behavior of the plant with respect 

 to soil acidity may be seen at a glance. In most Ericaceae the curves 

 indicate that there is a definite limit to growth on the less acid side, 

 and sometimes on the more acid side as well. There is also in most 

 cases a maximum in the curve, — an intermediate point — at which 

 the species is observed to grow with such frequence and luxuriance 

 that this value is to be regarded as its optimum reaction under 

 natural conditions. 



Each species has been examined, on the average, at 10 localities 

 selected so as to show as wide a range of conditions as possible. 

 Tests have been made at each locality in sufficient number to insure 

 the records being typical of the occurrence. Identifications of the 

 plants have been made with care, specimens of each being preserved, 

 and in cases of uncertainty submitted to authorities on the groups 

 concerned. While freely admitting that there is room for additional 

 data from other regions the writer feels that in most cases observa- 

 tions enough have been made to justify accepting with some degree 

 of confidence the definiteness of the optimum and limiting reactions 

 indicated. 



The American code of Nomenclature is followed for the most 

 part; but the genus-splitting favored in Britton and Brown's 

 "Illustrated Flora" and the "North American Flora" is not accepted. 



^Rhodora, 21 : 43 1920. 



