340 THE JOURNAL OF BOTANY 



form, that on an average nearly two new named forms appeared 

 for each one akeady admitted to our northern flora." The 

 num])er of novelties is to some extent due to "the great con- 

 servatism of Engelmann," wdiich "had not only caused him to 

 withdraw segregates of P. flavescens that he admitted at one 

 time, but had reacted on his early colleague Torrey, to the extent 

 of causing a number of mistletoes which had been designated in 

 the Torrey herbarium as new species to lie there, as they still 

 do, without publication." 



The material now contained in the great herbaria shows a total 

 of 277 " differentiable forms," of which 240 are regarded as species: 

 of these 66, or 23 per cent., are represented in the north, and 211, 

 or 77 per cent., in the equatorial region. Professor Trelease regards 

 these, which he terms respectively Boreales and iEquatoriales, 

 as " two primary groups, respectively constantly without and 

 with cataphyls on their foliage shoots " ; "of the Boreales 41, 

 or two-thirds, and of the iEquatoriales 87, or two-fifths, are now 

 characterised as new." The introduction, from which we take 

 this information, includes also an analysis of characters, and a 

 note on nomenclature, from which we learn that "the American 

 principle 'once a synonym always a synonym' " has been followed : 

 those who follow^ the general practice in this matter must there- 

 fore not accept Professor Trelease's names without investigating 

 their claims to adoption. 



It is obvious that only those intimately acquainted with the 

 genus could competently criticize the treatment of the species : 

 the present writer has no such qualification, and must therefore 

 content himself with saying that the descriptions are evidently 

 drawn up with great care, and that the enumeration of the 

 specimens examined, sometimes extending to a whole page, 

 shows that the author has had at his disposal a vast amount 

 of material. A clavis is given to the species of each section ; 

 there is a full synonymy of the older species ; there is a complete 

 index, collectors' numbers with identifications, and an index of 

 excluded species and of names : in the latter we think it would 

 have been useful had the novelties been indicated by an asterisk, 

 and had the principal reference been printed in black type. It 

 w^ould also have greatly added to the convenience of those 

 engaged in herbaria had each species received a number — as it 

 is, those who arrange the genus by the monograph will have to 

 add this for themselves. 



It remains to say a word about the plates, all of which are 

 reproduced from photographs, when possible from types. " Every 

 species has been figured, and scarcely a half-dozen types, even 

 of synonyms, are unpictured " : this has been rendered possible 

 by the co-operation of those in whose charge the types are placed, 

 t o whom Professor Trelease expresses grateful acknowledgement ; 

 237, or nine-tenths of the recognized forms, are now figured for 

 the first time. 



It is impossible to conclude the notice of this important 

 volume without a feeling of envy of our transatlantic colleagues 



