REVIEWS 499 



groups of chemical substances encountered in plants are briefly considered, 

 together with the types of synthesis involved in their production. 



The second chapter treats of the colloidal state, in illustration of which 

 nine experiments are described. Of these five are devoted to methods of 

 preparation of sols, gels, emulsoids, and suspensoids, and the remaining 

 four to illustrate precipitation by electrolytes, dialysis, and Brownian move- 

 ment. No experiments are, for example, suggested upon the changes in 

 volume of gels, their relation to absorption and diffusion, and the many pro- 

 perties which chiefly interest the biologist. Indeed, the practical work 

 on this important section appears to us very inadequate. 



The subsequent chapters treat of Enzyme Action ; Carbon Assimilation ; 

 Carbohydrates and their Hydrolysing Enzymes ; the Fats and Lipases ; 

 Aromatic Compounds and Oxidising Enzymes ; the Proteins and Proteases ; 

 the Glucosides and Glucoside-splitting Enzymes ; and the Plant-bases. 



Each chapter is followed by a bibliography, and a useful index is pro- 

 vided. 



In all, 158 experiments are described, with instructions that are to be 

 commended for their clarity and attention to detail. 



These pages undoubtedly supply a distinct need for which teachers and 

 students will alike be grateful. In such a work the choice of experiments 

 is largely a matter of opinion, but we venture to think that many will agree 

 in regretting that the authoress did not see fit to include experiments of a 

 quantitative character. To the student of Botany, for whom these pages 

 are primarily intended, the mere extraction and recognition of the chemical 

 substances within the plant is a very necessary preliminary, but it is the 

 chemical and physical properties on which his chief interest centres, and 

 for the investigation of which he would welcome a practical guide. 



E. J. S. 



A Manual of the Timbers of the World ; their Characteristics and Uses. By 



Alexander L. Howard. (Pp. xvi 4- 446 with 128 Illustrations.] 

 (London : Macmillan & Co., 1920. Price 30s. net.) 



The major part of this volume is occupied by a catalogue of timbers from all 

 parts of the world. In all, some 350 different commercial timbers are dealt 

 with, and it is an interesting sidelight on the need for much more work and 

 many more workers in this field of Economic Botany, that nearly 10 per cent, 

 of the timbers here enumerated are derived from unknown sources. When it 

 is remembered that these are mainly a selection of the better-known woods 

 it will be realised how deficient is our knowledge in respect to those less 

 familiar as commercial products. 



The author has aimed at completeness so far as the timbers upon the 

 European markets are concerned. That such a restriction was necessary is 

 obvious when we remember that Australia alone produces some four hundred 

 timbers, whilst those of North America are even more numerous. 



For most species data is furnished regarding the weight of a cubic foot of 

 the dry wood, the country of origin, and the technical characteristics, uses 

 and qualities. The author's forty years' experience in the timber trade gives 

 to the last an especial value. 



At several points Mr. Howard has some pertinent remarks to make on 

 British timbers. Referring to the Austrian method of cutting oak into billets 

 and wainscot wood, he says, " With the foreign oak the best methods to suit 

 the particular requirements of this country have been found, and acted upon, 

 but there have been no such wise methods employed with the ' home-grown ' 

 product." 



English ash suffers in comparison with that from France owing to the 

 more efficient forestry in the latter country, a criticism that the author might 

 have levelled with ec^ual justice against English oak. 



