— 77 — 



sedulously suppressed or re-baptised. This, the author contends, is to be avoided 

 by field study, by allowing a range of normal variation. He is rather severe on 

 men like Dr. Warnstorf, who lean on herbarium specimens for an excuse to multi- 

 ply varieties. Especially in the Sphagna does he urge and practice collecting and 

 preserving series. His dictum is "The study of forms is not labor lost. Who- 

 ever neglects this task, errs." And he declares that only the thorough field 

 student, who acquaints himself with physical and climatic influences on organic 

 life becomes able to elaborate the relation of mosses to all nature in a general Bryo- 

 geography. One understands after this consideration, why the author's chap- 

 ters, in the first part, on climatic influences, and geognostic relations of mosses 

 are so full of living interest. His observations on hygrophile, skiophile, photo- 

 phile messes; on mosses seeking calcareous soil, siliceous soil, salt soil, humus, 

 rocks of various composition, black and light colored soil, wet and dry soil, shady 

 .and sunny soil, bark and wood, on city pavements and in villages — all give a 

 deeper insight into the conditions of the life of mosses. 



In this whole work the idea of species-making is subordinated to the study 

 •of life conditions. The numbered systematic list of 536 species in the first part 

 is given merely to show their distribution in the four zones he establishes in his 

 area. 



In the second, the systematic part, which is accompanied by a map showing 

 the distribution of the Sphagna, Dr. Roell scores with amusing mildness the 

 reprehensible practices of certain bryologists — and other botanists — of juggling 

 with plant names largely for the purpose of getting their names attached to new 

 combinations. In no real sense is any botanist the father of a new combination 

 when he has simply transposed specific names to a new genus, rightly or wrongly. 



The problem of varieties receives intelligent attention also here, as must be 

 expected from so keen an observer of mosses in the field. Unfortunately we can- 

 not here enter into details. After discussing the rise of varieties in the last section 

 of part one, the author has a closing chapter on "Explanations by the Darwinian 

 Theory." While he finds that it is possible to explain many phenomena in 

 mosses, especially in the Sphagna, by the struggle for existence, by adaptation 

 to external influences, and the subsequent heritability of acquired characters, 

 ■etc., this theory is still not sufficient to explain many other facts, and he concludes 

 with the reflection that " Natural Science is not called upon to explain everything, 

 but must often be content with the establishment of that which Nature offers for 

 study," In this establishment of the facts of Nature, Dr. Roell has rendered 

 surely a notable service. 



The nomenclature of Sphagna is discussed with great detail. In the first 

 part, referring to the North American Flora, Dr. Roell expresses satisfaction over 

 the reduction of numerous Warnstorfian "herbarium species" of this genus edited 

 by Prof. A. LeRoy Andrews of Cornell; and while he approves on the whole 

 Andrews' treatment of this genus, he disagrees with the treatment of the Subse- 

 cunda group. 



In the general question of nomenclature Dr. Roell goes with Brotherus, S. O. 

 Tindberg, and Limpricht. He recognizes in the class Musci three subclasses, 



