6 LACTARIAE ОЕ THE UNITED STATES 
then, very strong, and the most pronounced differences are physio- 
logical and are lost in the dried specimens. 
In the present paper I propose to arrange the species of the 
genus in seventeen natural groups, each group being centered about 
a spécies which, by reason of possessing in a marked degree the 
characteristics found in the other species, shall stand as the type of 
the group. In many instances, the first described species has been 
found to combine the most of these characteristics. In speak- 
ing of this as a natural arrangement, I mean that each group is 
made up of those species which seem to be most closely related 
both morphologically and physiologically, and often so closely 
resemble each other as to be confused by the casual observer. 
In many groups the relationship is so marked that it is easy to 
conceive of the species as mutants from the type. Itis a grouping 
which deals primarily with the living plants. 
These groups I have in turn segregated into five sections: 
Piperites, Sublimacina, Limacina, Russularia,and Dapetes. Each of 
the last two embraces the species included by Fries in his so- 
called “‘tribe’’* of the same name. Оп the other hand, the species 
which he included under the “ tribe" Piperites, I have classified in 
three sections of equal rank with Dapetes and Russularia. The 
section Suó/imacina is made up of species possessing characteristics 
of both the Piperites and the Limacina. It is not intended that this 
grouping shall multiply the names to be used in classification, but 
that it shall be an aid in the determination of species and in the 
comprehension of relationship. 
THE DISTRIBUTION OF THE LACTARIAE IN THE UNITED STATES 
AND THE RELATION OF DISTRIBUTION TO LATITUDE, 
ELEVATION, AND FOREST CONDITIONS 
Some Lactariae have been reported from all of the states east 
of the Mississippi River excepting Illinois and Kentucky. In the 
region west of the Mississippi, fourteen species have been reported 
from Missouri, three from Капзаз.? two from Colorado, one from 
Nebraska, and ten from California.t This apparently limited dis- 
* According to our - present conception of the term tribe, Fries used it it incorrectly. 
He applied the name to each of the four groups into which he divided the genus, 
namely: Piferites, Dapetes, Russularia, and Pleuropus. Hym. Eur. 422-439. 1821. 
T I have seen only one specimen from Kansas and only a few from California. 
