2 BOTANICAL GAZETTE [JANUARY 
RETUSAE, and RetTIcULATAE. I shall not deal with the forms of 
sect. CORDATAE because C. R. Batt, the well known salicologist 
at Washington, D.C., has already undertaken a monograph of this 
special group. Should anyone else be interested in a special study 
of any other section or group of the North American willows I 
should be very glad to hear from him. 
In this article I intend to discuss the lions known from 
Mexico, Central America, and South America. There are among 
them many forms which, in my opinion, need a careful study in 
the field, and which are more or less closely related to forms from 
the southern parts of the United States. So far as I know, there 
has never been an attempt to give a critical review of these willows, 
but it seems to me impossible to determine any Mexican willow 
without having tried to interpret properly the species already 
described from that region. 
I wish to express my thanks to the gentlemen in charge of the 
following herbaria for the opportunity to study the material con- 
tained in the different collections: Herbarium of the Arnold 
Arboretum, Gray Herbarium, Herbarium of the Missouri Botanical 
Garden, Herbarium of the New York Botanical Garden, and the 
United States National Herbarium at Washington. 
The last enumeration of the Mexican willows was given by W. B. 
HemsSLeyY (Botany, Biol. Central. Amer. 3:179-180. 1883), but 
there is no critical examination of them. Since then several new 
species have been described by O. v. SEEMEN and by W. W. Row- 
LEE, which partly, as will be shown in the following notes, are 
founded on a wrong interpretation of already existing species. 
Unfortunately, the types of most of those species are in European 
herbaria, and I have not been able to examine them, especially the 
types of the species established by MARTENS and GALEOTTI mostly 
on sterile branches. In consequence of this lack of important 
material [ am not sure that my interpretation is correct in every 
case. Not only a careful study of the type specimens but also a 
more careful investigation of most of the species in the field is 
needed, and it is indeed the main purpose of this paper to draw 
the attention of all interested in the flora of Mexico and South 
America to what is still unknown of the willows of those countries. 
