species are but scantily represented. The Mexican boundary is so
unnatural a dividing line in the distribution of Cactaceae 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 preliminary 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 which will prove to be but
different phases of a single species.

In the matter of generic delimitation we are in still greater
uncertainty, 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, 1891.