THE FLORA OF NORTH AMERICA. 253 
wrong. In the year 1878, my colleague, Mr. Watson, 
finished and published his “ Bibliographical Index to the 
Polypetale 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 “ Gamopetale after Composite” in 
the ‘“‘Synoptical Flora,” brought out in the same year, con- 
tains 1656 species. The two together must make up half of 
our phenogamous 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 Pheno- 
gams and Ferns. My impression is that the species of Com- 
posite have increased at a rate which, unless they exceed the 
eight part of our Phznogams, 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 ;! 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. 
