136 THE PI.ANT WORI.D 



matter. In spite of this, however, we believe that many will be led to 

 turn their attention to this fascinating group of plants, the lichens. 



Several preliminary chapters are concerned with general considera- 

 tions, including the history of lichenology, the uses and nature of lichens, 

 their morphology, physiology, and geographical distribution, to which 

 are added directions for their collection and preservation. The second 

 part of the book is devoted to a manual of genera and species. The 

 determination of the genus is facilitated by means of keys, in the 

 making of which it had been better to use microscopic characters, if that 

 is possible. 



We fear that the author does not help the cause of science nor of 

 human interest when he speaks of lichens as ' ' the most altruistic of all 

 living organisms, since they live wholly for the good of others." We 

 are not justified in imputing to plants the virtue of self-sacrifice. So 

 far as our knowledge goes, we are led to believe that lichens do live 

 wholly for themselves, and are in no manner excepted from the general 

 necessity of struggling for existence. 



Several plates are devoted to the representation of structural and spore 

 characters, which will help students in the work of identification. 



For the aid of beginners, the publishers offer for sale sets of fifteen 

 representative species of crustose, foliose, and fruticose lichens, fully 

 named. The price is $1.75 the set. f. e. l. 



Bacteria, Yeasts, and Molds in the Home. By H. IV. Conn. 



pp. 6 + 293, illustrated. Boston : Ginn & Co., 1903. $1.00. 



Professor Conn, the well-known bacteriologist, has given us in this 

 book a very simple, popular but nevertheless scientific account of the 

 various organisms named in the title, which are of interest to us because 

 of their direct economic and hygienic importance. This account is not 

 simply descriptive of the organisms, but of their activities as well, and is 

 accompanied by an exposition of hygienic principles stated clearly, and 

 based upon knowledge of causes. The scope of the book is indicated 

 by the following : molds, their nature and conditions of growth, their 

 role in causing decay and disease, and their useful products ; yeasts, and 

 the phenomena of fermentation ; bacteria, their physiology ; preservation 

 of foods ; ptomaine poisons ; diseases of bacterial origin ; contagious 

 diseases and their prevention, together with many practical hygienic 

 suggestions. In an appendix of 18 pages are given a number of simple 

 outlines for bacteriological study. The volume is well printed and well 

 illustrated. It should be found on the school reference shelf and could 

 very well be used as a book for reading for high-school students. This 

 is true, not alone because of the clearness of exposition, but also because 

 of the emphasis laid upon accurate knowledge of causes. f. e. l. 



