102 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 13, NO. 6 
colloids are more important than the inorganic in furnishing hydrogen- 
ion to be neutralized by lime. The lack of relation between Ps and 
organic matter is not opposed to this, for the amount of organic 
acids needed to yield the Px values shown is infinitesimal in comparison 
with the total organic content. 
Summary.—In this paper lime-requirement is stated in parts per 
thousand of CaO; and, because of the ease with which relative values 
can be appreciated, active soil acidity is stated in the form of specific 
acidity. The ratio between these in a given soil may be expressed by 
a correlation coefficient C obtained by the equation: L.R. = C X 
(S.A. — 1). The value of C is believed to be a measure of the adsorp- 
tive power of the soil colloids for hydrogen-ion. 
The coefficient C has been found to vary so widely from one soil to 
another, from an untreated to a limed soil, and even from one depth 
to another in the same soil, that it is impracticable to calculate lime- 
requirement from acidity determinations in general, as has been 
proposed. Soils may be roughly classified on the basis of the value of 
C, a convenient ratio between classes being 10; but only if some 
simple procedure is first devised for classifying a given soil can there be 
obtained from its specific acidity a value for its lime-requirement. 
BOTANY.—Two new genera related to Narvalina. S. F. Buaxg, 
Bureau of Plant Industry. 
The type species of Narvalina, N. domingensis (Cass.) Less., is a 
shrub known only from the island of Hispaniola (Santo Domingo) 
in the West Indies. It is closely allied to the widespread and variable 
genus Bidens to which our “sticktights” or “devil’s pitchforks’’ belong, 
being distinguished chiefly by its shrubby habit, coriaceous leaves, 
and wing-margined achenes. Although still rare in herbaria, at least 
in this country, it is represented in the National Herbarium by two 
sheets of excellent specimens collected by Mr. Emery C. Leonard, 
who accompanied Dr. W. L. Abbott on a collecting trip to Haiti in 
1920. 
Up to 1900 only the original species had been referred to the genus. 
In that year three new species were described from Ecuador by the 
German student of Asteraceae, Georg Hieronymus. All three are 
now represented in the U. 8. National Herbarium by fragments of 
the types recently received from Berlin. Study of these fragments, 
consisting of fruiting heads accompanied by portions of the leaves, 
shows that they represent two rather remarkable new genera. 
