54 THE JOURNAL OF BOTANY 



but in certain cases, e. g. Phragmidmm disciflorum, there seems to 



have been a shght misunderstanding as to what those Eules entail. 



A useful index of host plants, one of the species, a list of excluded 



species, a glossary, and a bibliography — not so complete as one 



would wish— complete the volume. The name of the publishers 



is sufficient guarantee of attractive printing and binding. The 



line drawings (there are also a few wash drawings) are clear. 



Mr. Grove has compiled a book, reasonable in price, which must 



be in the hands of all British mycologists. t -n 



•^ *=■ J. Eamsbottom. 



Gruppe7itoeise Arthildung. By Hugo de Vries. 8vo, pp. viii. 

 365, with 121 figs, and 22 coloured plates. Borntraeger, 

 Berlin. 1913. Price 22 Marks. 



More than ten years ago in his Mutations-Theorie De Vries 

 endeavoured to show that the production of new species was, like 

 any other physiological process, a matter for experiment. Much 

 work has been done on the subject since then by De Vries him- 

 self. Dr. E. Gates, and others, especially in relation to the genus 

 CEnothera, investigations on which played so important a part in 

 De Vries's original memoir. The present remarkably w^ell-illus- 

 trated volume details the results of a large number of experimental 

 crossings between species and forms of CEnothera and the relation 

 of these results to the author's theory of the origin of species by 

 mutation. 



The text is divided into five sections. The first, entitled "The 

 Origin of Species through Mutation," is an exposition of the 

 author's views on mutations in the light of his theory of intra- 

 cellular pangenesis. The pangens are contained in the nucleus, 

 and have each their special character. Their condition varies, 

 and may be active, inactive, or labile, and the last-named state is 

 the cause of the conditions requisite for mutability. Section ii. 

 deals with " Keciprocal and Double-reciprocal Hybrids." The 

 author points out that the products of reciprocal crosses are very 

 often unlike, indicating that the characters contained in the pollen 

 differ from those in the egg-cell. Such species De Vries terms 

 heterogamous in contrast with isogamous species, in which pollen 

 grain and egg-cell bear the same characters. By the process of 

 gamolysis — that Is, the determination of these special characters 

 by crossing — De Vries seeks to analyse the constitution of 

 numerous natural species as well as mutants. Sections iii. and iv. 

 are respectively headed " Twin-hybrids " and " The Pangenetic 

 Investigation of New Species," and Section v. is a general dis- 

 cussion on the " Causes of Mutation." Appended are a biblio- 

 graphy of the literature of the subject since 1903 and a systematic 

 list of the crossings in the genus CEnothera which are described 

 in the text. 



The book is an important contribution to the study of genetics ; 

 and not the least useful features are the series of photographic 

 blocks with which the text is illustrated and the well-executed 

 coloured plates at the end of the volume. ABE 



