PREFACE. 
The present issue of the Contributions is made up of miscellaneous 
papers. The first three are continuations of studies published earlier 
in this series respectively on the Cactaceae, Crassulaceae, and Apiaceae, 
families which have presented unusual difficulties to botanists, and to 
which Dr. J. N. Rose, Associate Curator of the National Herbarium, 
has devoted special study in collaboration with Dr. N. L. Britton, of 
the New York Botanical Garden, and Prof. John M. Coulter, of the 
University of Chicago. The last paper, by G. N. Collins, Assistant 
Botanist in the Department of Agriculture, is an account of a remark- 
able development in a maize plant grown in a temperate climate from 
seed produced in the tropics. It is a suggestive illustration of the 
effect of environmental change. 
These papers form the concluding part of Volume XII of the 
Contributions. The title-page and index of the volume will be issued 
later. 
Freperick V. CoviLur, 
Curator of the United States National ITerbarium. 
Tit 
