109 



and illustrate most excellently the visible effects of interaction 

 between cells, which is a point of particular interest especially in 

 relation to the expression of such characters as leaf-shape. The 

 evidence that S. Darwinianum is a true fusion hybrid is not 

 given. All this data is certainly well known by the authors, as is 

 indicated by the discussion on page 148, but the treatment is 

 hardly clear to one not already fully acquainted with the litera- 

 ture of the subject. 



The bibliography includes no reference later than 191 2, and in 

 the list of books on plant-breeding there are some noticeable 

 omissions of which we may mention Cramer's Kritische Ubersicht 

 der hekannten Falle von Knospenvariation published in 1907 and 

 the recent volume by de Vries entitled Gruppenweise Arthildung. 



The reviewer is in full sympathy with the purposes of the 

 volume, with the excellent selection of the subject matter, and the 

 interesting presentation which gives to volumes of this kind a 

 well-deserved popularity. 



The defects of the volume are those that are common to Amer- 

 ican text-books and popular treatments of scientific subjects. 

 It seems to be the rule that the presentation must be simple and 

 definite with little if any critical analysis of facts and theories, 

 a treatment which gives an unwarranted air of finality and 

 authority not in harmony with the subject itself and not stimula- 

 tive to an attitude of inquiry on the part of the average reader. 



A. B. S. 



Illick's Pennsylvania Trees * 



This is an excellently conceived book of 231 pages, of which 

 the first 52 pages. Part I, "is intended for the layman and the 

 beginner of forestry" and "comprises abstracts from the author's 

 lectures on elementary forestry at the Pennsylvania State Forest 

 Academy." This part is neatly and comprehensively illustrated 

 by numerous photographs and drawings, and constitutes a simple 

 and compact treatment as to general considerations of the 

 economic value, natural and artificial development, and eco- 



* Pennsylvania Trees, by J. S. Illick, professor of dendrology and forest manage- 

 ment, Pennsylvania State Forest Academy. Bull. No. ii, Penn. Dept. Forestry, 

 Harrisburg, Pa., 1914. 



