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make a more satisfactory presentation possible. It would be useless to 
notice the vast number of reputed species that are not represented by 
actual specimens in our possession, 
In the proposed preliminary account of the family, of which the present 
paper is the first part, only those genera are considered which form a part 
of the flora of the United States, and those species which I have been 
able to examine and to identify with reasonable certainty. All forms 
credited to the United States have been studied, and the account of these 
species may be considered fairly complete, but the far more numerous 
Mexican species are but scantily represented, The Mexican boundary 
is so unnatural a dividing line in the distribution of Cactacez that it 
has been disregarded, and all the species studied have been arranged in 
a lineal series of uniform prominence. So far as known the subject of 
geographical distribution is considered, but it will be seen how meager 
is our knowledge of this subject. It is to be hoped that this prelim- 
inary presentation will provoke exploration and study, and that species 
will not only be collected, but all the facts of their distribution noted. 
It is more than probable that our present notion of species in this 
group must be much modified, and doubtless many forms are at present 
kept specifically distinct w hich will prove to be but different phases of 
a Single species. 
In the matter of generic delimitation we are in still greater uncer- 
tainty, and several generic lines at present recognized must be regarded 
as purely arbitrary, a fact which must become still more evident with 
additional material. The whole group is to be regarded as made up of 
poorly differentiated forms and only long observation under cultivation 
can determine the possibilities of specific variation under the influence 
of environment, of age, of inherent tendencies. For instance, that 
these plants change in form and in spine characters with increasing 
age and after they have begun to flower can not be doubted, but what 
described forms have thus been separated in descriptions can only be 
guessed at. 
JOHN M. COULTER. 
LAKE Forest UNIVERSITY, 
Lake Forest, Ill., January, 1894, 
