THE FLORA OF NORTH AMERICA. 253 



wrong. In the year 1878, my colleague, Mr. Watson, 

 finished and published his " Bibliographical Index to the 

 Polypetalae of North America," covering, that is, the same 

 ground as the first volume of Torrey and Gray's Flora, com- 

 pleted in 1840. In it the 2200 species of the latter date are 

 increased to 3038. The " Gamopetctice after Composite n in 

 the " Synoptical Flora," brought out in the same year, eon- 

 tains 1656 species. The two together must make up half of 

 our phaenogamous botany, that is, adding the increase of the 

 last four years, about 5000 species. And so Mr. Watson 

 adopts the estimate of 10,000 species of our known Phaeno- 

 gams and Ferns. My impression is that the speeies of ( 'om- 

 positce have increased at a rate which, unless they exceed the 

 eight part of our Phaenogams, will warrant a still higher esti- 

 mate. The number of introduced species of various orders, 

 which will have to be enumerated and most of them described, 

 is, unhappily, fast increasing; 1 and new indigenous species 

 are almost daily coming to us from some part or other of our 

 wide territory. So that the 10,000 species of this estimate 

 may before long rise to eleven or twelve thousand. Only the 

 experienced botanist can form a just idea of what is involved 

 in the accurate discrimination and proper coordination of 

 10,000 to 12,000 species, and in the putting of the results into 

 the language and form which may make our knowledge avail- 

 able to learners or to succeeding botanists. 



Moreover, there is of late an embarras des richesses which 

 is becoming serious as respects labor and time. The con- 

 tinued and ever increasing influx of material to Cambridge, 

 beneficial as it ever is, is accountable for this retardation of 

 progress in a greater degree than almost any one would sup- 

 pose. The herbarium, upon whose materials this work is 

 mainly done, and which has been, like the Temple, full forty 

 and six years in building, has received the contributions of 

 two generations of botanists, and the Torrey herbarium goes 

 back one generation farther. Still the number of American 



1 I say " unhappily," for they adulterate the natural character of our 

 flora, and raise difficult questions as to how much of introduction and 

 settlement should give to these denizens the rights of adopted citizens. 



