254 ESS A YS. 



specimens annually coming to it is greater than in most for- 

 mer years. Apart from the mere selection and care of these, 

 consider how in other ways it affects the rate of progress of 

 the Flora. The incoming of additional specimens may at a 

 glance settle doubt as to the validity of a species ; but new 

 specimens are as apt to raise questions as to settle them ; more 

 commonly they raise the question as to the limitation and 

 right definition of the species concerned, not rarely, also, that 

 of their validity. When one has only single specimens of re- 

 lated species, the case may seem clear and the definition easy. 

 The acquisition of a few more, from a different region or 

 grown under different conditions, almost always calls for some 

 reconsideration, not rarely for reconstruction. People gener- 

 ally suppose that species, and even genera, are like coin from 

 the mint, or bank notes from the printing press, each with its 

 fixed marks and signature, which he that runs may read, or 

 the practised eye infallibly determine. But in fact species 

 are judgments — judgments of variable value, and often very 

 fallible judgments, as we botanists well know. And genera 

 are more obviously judgments, and more and more liable to 

 be affected by new discoveries. Judgments formed to-day — 

 perhaps with full confidence, perhaps with misgiving — may 

 to-morrow, with the discovery of new materials or the detec- 

 tion of some before unobserved point of structure, have to be 

 weighed and decided anew. You see how all this bears upon 

 the question of time and labor in the preparation of the Flora 

 of a great country. If even in Old Europe the work has to 

 be done over and over, how much more so in America, where 

 new plants are almost daily coming to hand. It is true that 

 these fall into their ranks, or are adjustable into their proper 

 or probable places, but not without painstaking and tedious 

 examination. 



Of our Flora, it may indeed be said, that " If it were done, 

 when 't is done, then 't were well it were done quickly." 

 But I may have made it clear that, in the actual state of the 

 case, it is likely to be done slowly. At least you will under- 

 stand why thus far it has been done slowly. As to the future, 

 if it depended wholly upon me, the completion would obvi- 



