PREFACE. 



The first of the accompanying papers, by J. N. Rose and Paul C. 

 Standley, deals with the Mexican species of Talinum, a genus of portu- 

 lacaceous plants which has been much neglected in the past, only a 

 few species having been known from Mexico. Studies of living plants 

 in Washington and of accumulated herbarium material, however, have 

 enabled the writers to revise all the proposed Mexican species of the 

 genus and make numerous additions. Of the eighteen species here 

 recognized, ten are new to science. 



The second paper, by J. N. Rose, records two additional species of 

 the recent umbelliferous genus Harperella. 



Frederick V. Coville, 

 Curator of the United States National Herbarium. 



