April 29, 1922] 



NATURE 



547 



rewritten, and some of the inadequate practical details 

 have been amplified. The chapter on the ultramicro- 

 scope stands out, as before, as one of the best in the book, 

 and the later apparatus of Zsigmondy is here described. 

 Moreover, the book is clearly printed in good-sized type, 

 and the illustrations, although only the reproductions 

 of line drawings, are unusually good for this class of 

 figure. A. E. H. T. 



(i) Photo-Engraving Printer : Concise Instructions for 

 Apprentice Engravers or for those seeking simple yet 

 practical knowledge of Line and Half -Tone Engraving. 

 By S. H. Horgan. Pp. xvi + ioo. (London: P. 

 Lund, Humphries and Co., Ltd., 1921.) 55. net. 



(2) Byepaths of Colour Photography. By 0. Reg. 

 Edited and with an Introduction by William Gamble. 

 Pp. xii + ii6 + xiii-xx. (London: P. Lund, Hum- 

 phries and Co., Ltd., 1921.) 55. net. 



Both these volumes are by " practical men," and they 

 are characterised to the full, if we may say so, by the 

 advantages and the disadvantages that might be 

 expected to result from this fact. Each has a critical 

 and, to a certain extent, supplementary introduction 

 by Mr. W. Gamble, so that the reader may feel fully 

 assured that he is in safe hands, (i) Mr. Horgan goes 

 clearly and concisely over the subject as he has practised 

 it, and as he is a man of great and prolonged experience, 

 his instructions cannot fail to be of value to the student, 

 whether or not he has arrived at the stage of workman. 

 But it is not a treatise on the subject. The author 

 leaves theory quite on one side, though here and there 

 he justifies his directions by a shrewd statement of the 

 trouble likely to follow variations of them. Perhaps 

 the chief matter to notice is that Mr. Horgan uses 

 collodion, while in this country gelatine plates have 

 largely replaced it. 



(2) Mr. Reg clearly describes his own system in which 

 he uses a one-exposure camera, with one reflector and 

 one compensator, and plates specially sensitised. He 

 gives full details as to the making of the camera, 

 formulae for sensitising the plates, and instructions for 

 the general procedure. Rather more than half the 

 volume is devoted to throwing what he calls "side- 

 lights " on certain notions of previous inventors. 

 Here he is not always lucid, and his excursions into 

 theor)' are not always fortunate. But he has been a 

 diligent searcher with regard to the methods of other 

 workers in this field, and gives many useful dates 

 and references to patents, with illustrations of 

 apparatus. He calls his volume " byepaths," and in 

 this sense it is both useful and interesting. C. J. 



Forestry for Woodmen. By C. 0. Hanson. Second 

 edition. Pp. 238 + 13 plates. (Oxford : At the 

 Clarendon Press, 1921.) 6i. 6d. net. 



During the ten years that have elapsed since the first 

 edition of this book was published, much progress in 

 the art of forestry has been made in this country. 

 The necessity of having within our shores an ample 

 store of growing timber to meet the possible emergency 

 of war, is now admitted by statesmen. The Forestry 

 Commission established in 1919 has been busily 

 engaged in acquiring land for new plantations and in 

 re-afforesting the extensive areas which were denuded 



NO. 2739, VOL. 109] 



of timber during the war. Municipalities are awaken- 

 ing to the useful work of covering their water-catch- 

 ment areas with trees, as evidenced by the new scheme 

 of the Glasgow Corporation, which, if carried out, will 

 create around Loch Katrine a magnificent forest, such 

 as that owned by Liverpool at Vyrnwy in Wales. 



The interest in forestry is increasing, and there is a 

 demand for elementary instruction on the subject. 

 This has been met by the publication of the second 

 edition of this useful manual. It is well adapted for 

 the purpose, being cheap in price, handy in form, and 

 simple in language. Scarcely any change has been 

 made in the original text, but two chapters have been 

 added. One deals with the Forestry Act of 1919 and 

 the Forestry Commission, and gives a summary of 

 recent developments. The other new chapter treats 

 briefly the afforestation of waste land, and gives a 

 sketch of the survey necessary before any planting 

 scheme can be decided upon. The book is brought 

 up to date by the intercalation of a new paragraph 

 here and there, and it may be recommended to land- 

 owners, as well as to agricultural students and forestry 

 apprentices, as a satisfactory guide to elementary 

 forestry. The index is, however, incomplete, and 

 should be enlarged to double its present size in a new 

 edition. 



Problemi di Filosofia Botanica. By Antonino Borzi. 

 Pp. 344. (Roma : G. Bardi, 1920.) 60 lire. 



The introduction of this posthumous work contains a 

 short historical sketch of vegetable biology, as fore- 

 shadowed by the elder Agardh, Delpino (to whose 

 memory the book is dedicated), Haeckel, and others. 

 The scope of the book itself is best indicated by the 

 chapter headings : I. General conceptions and limits 

 of vegetable ecology ; II. Ecological principle of 

 vegetable organisation ; III. Ecological principles of 

 vegetable associations ; IV. Ecology of dissemination ; 



V. Aerophylactic function in the vegetable kingdom ; 



VI. Hydrophylactic function in the vegetable kingdom ; 



VII. Form and evolution of the earliest vegetable life. 



VIII. Ecological conception of the evolution of the 

 vegetable kingdom. 



The author, a specialist on Cyanophycese, sums up 

 very ably in chap. vii. his observations on the evolu- 

 tion of that group, and describes their extraordinary 

 adaptability to varying ecological conditions. Con- 

 tinuous vegetative reproduction means a progressive 

 development, from which no return to an earlier stage 

 ever occurs ; but development of the sexual function 

 arrests such indefinite evolution and lays the foundation 

 of constant characters. " Mutation " occurs before the 

 development of sex. The polyphyletic origin exem- 

 plified in Cyanophyceae is also manifested in the scheme 

 of the entire vegetable kingdom. 



The view generally held, that subaqueous life repre- 

 sents the primitive condition of terrestrial vegetation is 

 regarded as unproved. Hydrophytes and aerophytes 

 are probably two distinct stocks, the former represent- 

 ing primitive vegetation, the latter originating as 

 Vascular Cryptogams at the period of land-emergence. 

 That Bryophytes may possibly be survivals of a 

 transitional stage between Hydrophytes and Aero- 

 phytes is not sufficiently clear. These views are set 

 forth in detail. 



