THE FLORA OF NORTH AMERICA. 251 



can plants was at no time pretermitted, either by Dr. Torrey 

 while he lived, or by myself, we were unable to continue the 

 publication during my associate's lifetime ; and it was only 

 recently, in the spring of 1878, that I succeeded in bringing 

 out, in a changed form, another instalment of the work, com- 

 pleting the Gamopetalce. 



In the interval I had made two year-long visits to Europe 

 for botanical investigation, the first partly relating to the bot- 

 any of the South Pacific, the second wholly in view of the 

 North American flora. And since this last publication still 

 another visit — the fourth and we may suppose the last — of 

 the same character and the same duration, has been success- 

 fully accomplished. 



The serious question, in which we are all concerned, arises, 

 whether this work can be carried through to completion, and 

 the older parts (wholly out of print and out of date), reelabo- 

 rated, — I will not say by my hands, but in my time, or soon 

 enough to render the whole a reasonably full and homogene- 

 ous representation of the North American flora, as known in 

 this latter part of the nineteenth century. And it brings us 

 to consider why the undertaking to which so much time has 

 been devoted should be so slow of accomplishment. 



If this slowness is a constant wonder and disappointment to 

 most people interested in the matter, I can only add that it is 

 hardly less so to myself. It is a constant surprise — if one 

 may so say — that the work does not get on faster. 



Of course the undertaking has become more and more for- 

 midable with the enlargement of geographical boundaries and 

 of the number of species discovered. As to the increase in 

 the number of species to be treated, we have by no means yet 

 reached the end. The area, that of our continent down to the 

 Mexican line, we trust is definitely fixed, at least for our day. 

 And since we cannot be rid of the peninsula and keys of Flor- 

 ida, which entails upon us a considerable number of tropical 

 species, mostly belonging to the West Indies — the southern 

 boundary is now as natural a one as we can have. 



The area which Pursh's Flora covered was, we may say, the 

 United States east of the Mississippi, with Canada to Labra- 



