390 NOTICES OF NEW BOOKS. 



sufficient for the identification of lichens. The Hchenist finds it more 

 and more necessary to include in his equipment a microscope with an 

 objective giving a considerable magnification. Spore measurements, 

 given in multiples of the micron, occur on every page of the text, and 

 drawings of highly magnified asci, paraphyses and spores appear on each 

 of the seventy-one plates at the end of the volume, which illustrate the 

 microscopical characters of typical species. 



The classification used is one based upon the form and structure of 

 the reproductive organs. British lichens are arranged in two great 

 series : (1) Gymnocarpere, the fruits of which have the form, more or 

 less, of an open disc ; and (2) Pyrenocarpese, with closed fruits. The 

 Gymnocarpese are further divided into three sub-series, each of which 

 has distinctive fruit characteristics. 



Another welcome and very helpful feature of this volume is the 

 series of keys to the genera. In the case where a genus includes a 

 large number of species a key to its sub-divisions has been added. 

 These keys have been frequently tested, so that it can be said of them 

 that they will prove a valuable time-saving aid for the identification of 

 unfamiliar species. Considerable thought and skill have been given in 

 the arrangement of this part of the book. 



To those who are more or less acquainted with the lichen flora of 

 Great Britain the changes in nomenclature and the re-arrangement of the 

 Orders (Families) will appear unfamiliar, but the very full list of 

 synonyms that follows the description of each species, sub-species, 

 variety and form, and the well-prepared index will enable the student to 

 trace any plant with the name of which he may be acquainted. As the 

 knowledge of British lichens accumulated, changes in nomenclature 

 became inevitable. 



The writer of this Monograph is to be congratulated on the successful 

 completion of so important a piece of work, a work that has occupied 

 several years of painstaking investigation and critical weighing of 

 evidence, possibly associated sometimes with the feeling of a heavy weight 

 of responsibility. 



The Completed Monograph of British Lichens becomes at once a 

 landmark in British Lichenology which will be for some time to come 

 the standard for reference. It will take a high rank among the several 

 excellent Natural History publications issued from time to time by the 

 Trustees of the British Museum. 



Robert Paulson. 



