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THE CACTACEAE. 



INTRODUCTION. 



The writers began field, greenhouse, and herbarium studies of the Cactaccae in 

 1904 and in the years following they made studies and collections over wide areas 

 in the United States, Mexico, and the West Indies. It was first intended that 

 these should be followed by a general description of the North American species 



but a plan for a more complete investigation of the family was proposed by 



Dr. D. T. MacDougal in J 



This was approved by the trustees of 



Carnegie Institution of Washington at its next regular meeting and a grant was made 

 to cover the expenses of such an investigation. Dr. Rose was given temporary 

 leave of absence from his position as Associate Curator in charge of the Division of 

 Plants, United States National Museum, and became a Research Associate in the 

 Carnegie Institution of Washington, with William R. Fitch and Paul G. Russell as 

 assistants; Dr. Britton, Director-in-Chief of the New York Botanical Garden, was 

 appointed an honorary Research Associate, while R. S. Williams, of the New York 

 Botanical Garden, was detailed to select and preserve the specimens for illustration. 

 Work under this new arrangement was begun January 15, 191 2, and thus several 

 lines of investigation were undertaken in a comprehensive way. 



1. Reexamination of type specimens and of all original descriptions: This was 

 necessary because descriptions had been incorrectly interpreted, plants had been 

 wrongly identified, and the errors perpetuated; thus the published geographical 

 distribution of many species was faulty and conclusions based on such data were 

 unreliable. Not only had specific names been transferred to plants to which they 

 did not belong, but generic names were interchanged and the laws of priority 

 ignored. Many valid species, too, had dropped out of collections and out of current 

 literature and had to be restored. 



2. Assembling of large collections for greenhouse and herbarium use: Extensive 

 greenhouse facilities were furnished by the New York Botanical Garden and the 

 United States Department of Agriculture, while the herbaria and libraries of the 

 United States National Museum and of the New York Botanical Garden furnished 

 the bases for the researches. The New York Botanical Garden has also cooperated 

 in contributing funds in aid of the field operations, in clerical work, and a large 

 number of the illustrations used have been made there, the paintings and line 

 drawings mostly by Miss Mary E. Eaton. 



3. Extensive field operations in the arid parts of both Americas: Many of these 

 deserts are almost inaccessible, while the plants are bulky and if not handled care- 

 fully are easily destroyed. Many plants require several years to mature, in some 



many years to flow 



Through these explorations were obtained 



the living material for the greenhouse collections and for exchange purposes, as 

 as herbarium material for permanent preservation. Of much importance, ; 

 were field observations upon the plants as individuals, their form, habit, hab 

 and their relations to other species. 



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