174 



eastern and western plants different species ? Or is this a 

 problem for the ecologist rather than for the systematist? 



In discussing some of the phytogeographical phenomena of 

 Europe Dr. Hilgard comments on the physical and chemical 

 theories of soil influences, and the classification of plants as " cal- 

 ciphile," " calcifuge," " silicophile," etc., and reviews the work of 

 Thurmann, Fhche, Grandeau, Bonnier, Contejean, A. F. W. 

 Schimper, Wahlenberg, and others. He also emphasizes the great 

 predominance of calcareous soils in Europe as compared with 

 America, a fact which is often overlooked by ecologists and 

 agricultural scientists when making use of European literature. 

 Another important point is that the definition of calcareous soils 

 differs considerably in the two continents. In Europe a soil is 

 not usually called calcareous unless it effervesces with acids, 

 which requires 4 or 5 per cent, of calcium carbonate, while in the 

 United States many soils bearing characteristic " lime vegetation " 

 contain less than i per cent, of the same mineral. 



The last chapter, on the vegetation of saline and alkali lands, 

 is based on some of the author's latest work in California. It 

 contains illustrations of several of the characteristic alkali plants, 

 with some anatomical and physiological notes, and statistics of 

 the maximum, minimum, and optimum amounts of the various 

 alkalies in the soil for each species. 



The three short appendices deal with simple methods of soil 

 examination. The subject index is as complete as could be rea- 

 sonably desired, and in place of a regular bibliography there is an 

 index of the names of authors whose works are referred to in the 

 text.* Among about 185 such names botanists will be interested 

 to see those of Coville, Darwin, Haberlandt, Kearney, Kuntze, 

 Mohr, G. T. Moore, W. J. V. Osterhout, and J. W. Tourney, be- 

 sides those mentioned above. 



If space would permit, a great deal more might be written about 

 this book, which must be seen to be appreciated. It will be very 



* Dr. Hilgard does not attempt to list his own writings on the subject, but the fol- 

 lowing references will be instructive to the reader who wishes to become more 

 familiar with his views: Science ii : 241, 242. 1888; Overland Monthly, D 

 1891 ; Science II. 18 : 755-760. D 1903 ; ig : 333, 234. 5 F 1904 ; 20 : 605- 

 608. 4 N 1904; 23: 70,71. 12 Ja 1906. 



