iv PREFACE. 
reasons, anything very closely approaching completeness could not have been attained 
had there been half a dozen workers in the field, instead of only one, the omission of 
some small historical collections is of the very slightest importance. Notwithstanding 
the fact that the work has been substantially restricted to the Kew Herbarium and 
Library, it has been, as already mentioned, considerably extended in a direction not 
originally contemplated. For the purposes in view it was thought that we might very 
largely rely on the names as we found them in the Kew Herbarium, and describe 
only such very evident novelties as did not involve too great an expenditure of time. 
In this manner the whole of the Polypetale was written out, and in the hands of the 
Editors, when an offer was received from Drs. Parry and Palmer to present the first 
set of a large collection of dried plants, chiefly from the State of San Luis Potosi, on 
the condition that we named the whole of them and embodied them in the “ Biologia.” 
To do this properly involved an enormous additional expenditure of time and money; 
yet the offer was accepted, and the writer, aided by his colleagues at Kew, spent 
nearly seven months on this collection, and the investigations it entailed, thereby 
greatly enhancing the value of the Enumeration, without considerably increasing its 
bulk. 
This critical examination of a large portion of the Mexican plants led to much fuller 
synonymy and references to the existing literature in the second and succeeding 
volumes than is given in the first, and we are fully justified in saying that the quality. 
of the work has improved in consequence. 
Although an immense amount of time has been spent in looking up published 
species not represented in the Kew Herbarium by authenticated specimens, some, 
doubtless, have been overlooked; but a few omissions are of little consequence. Had 
every name referring to a Mexican plant been taken up, the result would have been 
literary completeness, it is true, yet nothing more. Moreover, it would be mere 
affectation to apologize for shortcomings of this kind in a work professedly little more 
than a skeleton from the standpoint of a systematist. As explained in the Appendix, 
upwards of a thousand nominal species are left out of consideration in the geographical 
tables, because it is believed that their retention would swell the proportion of the 
endemic element beyond what it really is. 
