PREFACE. 



The fourtli installment of the Trees and Shrubs of Mexico, by 

 Mr. Paul C. Standley, Associate Curator of the United States Na- 

 tional Herbarium, treats the families Passifloraceae to Scrophu- 

 lariaceae. Several large families are included, notably the Cac- 

 taceae, of which Mexico possesses a far greater number of species 

 than does any other part of the earth. Other important groups 

 covered are the Myrtaceae, Melastomaceae, Asclepiadaceae, and Ver- 

 benaceae, families whose Mexican representatives have received 

 little systematic attention during the last 30 years or more. 



The account of the family Passifloraceae has been furnished by 

 Mr. Ellsworth P. Killip, and that of the Cactaceae by Dr. N. L. 

 Britton and Dr. J. N. Rose. 



FrEDEKICK V. COVILLE. 



Curator of the United States National Tlerhanum. 



