92 
not only critical remarks upon known species, but also the diagnoses 
of many unpublished species which had come into his hands, notably 
those collected by Mr. William Gabb in 1867 in Lower California, 
The collections that have thus far been studied are: 
(1) Those of the Missouri Botanical Garden; and thanks are espe- 
cially due to Dr. Trelease for his generous cooperation in the use of 
this material, without which the work would have been impossible. 
(2) Those of the Department of Agriculture, including the results of 
several recent explorations, for the use of which I am indebted to Mr. 
Frederick V. Coville. 
(3) Those of the Gray Herbarium at Harvard University, which Dr. 
B. L. Robinson kindly placed at my disposal. 
(4) Those of the California Academy of Sciences, notably rich in forms 
from Lower California and the adjacent islands, kindly loaned by Mr. T. 
S. Brandegee. 
(5) Those of Dr. Louis Eschanzier, of San Luis Potosi, Mexico, who 
sent a large series of Mexican forms collected in 1891. 
(6) Numerous small sets from different correspondents, who have 
given both time and material in aiding the work. 
It is needless to say that Dr. George Engelmann, the great pioneer 
student of this difficult family, has opened the paths in which we must 
follow, and it was exceedingly unfortunate that he was not able to com- 
plete the final revision that he had in mind. 
The difficulties which beset the critical study of this group can not 
easily be exaggerated. Such scanty material as has been collected has 
been for the most part very incomplete, consisting of plant bodies with- 
out flower or fruit, flower or fruit without plant bodies, and bunches of 
spines without either. The species are displayed also in the most inac- 
cessible regions, and their culmination is found in the still T poorly known 
regions of Mexico. 
On account of their singular forms and often brilliant flowers they 
have long been extensively cultivated, especially in Kurope. These cul- 
tivated forms have formed the basis of original descriptions in almost 
all of the European publications, and in very rare cases have any types 
been preserved. As a result, the bibliography of Cactacee is appalling, 
and it is questionable whether satisfactory conclusions can be reached 
in the case of hundreds of published names. The earlier descriptions 
were not only meager, but were based upon what are now regarded 
very insufficient characters, and in the absence of typesit is not only 
unsafe, but impossible to venture an opinion concerning their identity. 
In view of these facts, [ have thought it advisable to present a prelim- 
inary revision of the order, which shall contain the results of the study 
of material confessedly insufficient. With such knowledge as we pos- 
sess brought together, it is hoped that the study of this very interest- 
ing and much neglected group will be stimulated, and that more crit- 
ical exploration of our southwestern territory and adjacent Mexico will 
