INTRODUCTION. XXVil 



nated the aggregate, is too usually retained with a changed and 

 restricted meaning to designate A only ; other names being 

 found for B and C. Equally in this second class of cases a 

 confusion of nomenclature arises. The aggregate species ABC 

 may chance to be represented in an herbarium by specimens 

 of any one, or of two, or of all three segregates ; placed there 

 under one and the same name, that is, under the original name 

 which subsequently has come to mean A only ; while at a later 

 date other specimens of B and C may have been placed with 

 the former, and then labelled under their newer names. In 

 appearance, at some after time, there will be great confusion 

 among the plants and names, if examined by succeeding 

 botanists unprepared to apply the necessary explanations by 

 reference to past dates and name-changings. 



An example may again be useful in illustration of this. At 

 past dates, say 1830 1840, the name Potamoyeton natans may 

 have been written, without any real blunder or misnomer, on a 

 label attached to a specimen of Potamoyeton polygonifolius, or on 

 another connected with a specimen of Potamoyeton plantayineus. 

 These labels were correct according to the ideas of the species 

 formerly accepted, and even still so accepted as lately as the 

 date of Bentham's Handbook in 1858. But at more recent 

 dates, say between 1860 1870, and tested only by the views 

 about these plants subsequently accepted among us, the labels 

 might appear to be errors of names ; that is, unless the former 

 triple application of the one name natans were steadily kept in 

 recollection. A herbarium formed during the years 1830 1870 

 may thus represent any diversities of nomenclature currently 

 used in books during the same period, or even long antecedently, 

 according to the descriptive books relied on by the labellers. 



Besides those two sources of misnomer or, discords connected 

 with dates, rather than real errors of name there have been 

 purposely glued into the herbarium, here referred to, not a few 

 actual errors of name on the labels with specimens ; some of 

 them very wide errors indeed. Two useful ends were sought in 



