A.NUARV S, 



1922] 



NATURE 



was carried out during the war period when the 

 adequate examination of these products was a 

 matter of such great importance. Although most 

 ol the methods dealt with have already been de- 

 M ribed either in technical journals or in the pro- 

 I cdings of technical societies, chemists will wel- 

 come the accumulation of this information within 

 the covers of one volume. Moreover, the admir- 

 ihle summary of "The Constituents of Coal-tar 



id their Properties," compiled by Dr. Spielman, 

 appears in a revised form as an appendix, and the 

 inclusion of this information may prove useful to 

 the coke-oven chemist by saving reference 

 work. 



The rest of the book is disappointing. In de- 



ribing analytical methods the author has obvi- 

 ously attempted to do more than supply indica- 

 tions of the method recommended by him, but has 

 failed to furnish sufficient detailed information to 

 be of real service to the works chemist. 



The chapter dealing with the fractions of coal- 

 rar other than the naphtha fraction is meagre, 

 and the weakness of this section accentuates the 

 fact that chemists have not yet given adequate 

 study to the analytical methods required in the 

 examination of the heavier fractions of coal-tar, 

 which are no less important than the naphtha dis- 

 tillate. It is in this section of the book that a 

 recommendation appears which would have 

 shocked those older and well-established chemists 

 who attempted to teach us our subject, and who, 

 not living m these times of efficiency systems and 

 labour-saving devices, paid due reverence to in- 

 struments by which accurate measurements might 

 be made. The recommendation refers to the 

 crystallisation of crude tar acids, the instructions 

 being to cool the liquid, "stirring continually with 

 a Fahrenheit thermometer graduated in tenths of 

 a degree." 



The treatment accorded in other sections of the 

 book to the analy^s of gases, calorimetry, and 

 the examination of chemical products made and 

 required in the recovery works is all too brief. 

 The analysis of coal-gas, which is acknowledged 

 to be so intricate as to require considerable ex- 

 perience before trustworthy results can be ex- 

 pected, is dealt with in a few pages, whilst the 

 method of procedure recommended is archaic. 

 The estimation of naphthalene is carried out by a 

 method which would be quite unpractical. if small 

 quantities of ammonia were present in the gas, 

 though no mention is made of this fact. 



Finally, the manual contains the usual collection 

 of tables and conversion factors in the second 



)pendix — so useful to reader, author, and pub- 

 -licr. E. V. Evans. 



NO. l-Jll, VOL. 109] 



Lichens. 



(i) Lichens. By A. L. Smith. (Cambridge 

 Botanical Handbooks.) Pp. xxviii-f464. (Cam- 

 bridge: At the University Press, 1921.) 55s. 

 net. 



(2) A Handbook of the British Lichens. By Annie 

 Lorrain Smith. Pp. vii + 158. (London: The 

 British Museum (Natural History), 1921.) 

 65. 6d. 



(0 



FOR many years botanists have been with- 

 out a guide to the large mass of facts 

 that have been added year by year to our know- 

 ledge of lichens. Miss A. Lorrain Smith has 

 therefore done a good work in compiling a very 

 comprehensive handbook on this group of plants. 

 The growth of our manufacturing and even our 

 garden cities proves fatal to all except a few- 

 insignificant lichens. They are driven away to 

 those far-off parts of the country where the air 

 is still fresh and pure. This circumstance very 

 possibly, but the absence of any comprehensive 

 handbook on, and guide to, the lichens certainly, 

 is a reason why so little interest is taken in this 

 group. Yet, ecologically, it is one of the most 

 interesting groups. Lichens grow on the out- 

 skirts of vegetation, as pioneers of the plant world, 

 preparing the way for moss, fern and flowering 

 plant. They are most intimately in touch with 

 the substratum in its virgin condition. Few ecolo- 

 gists, however, properly consider lichens. Ana- 

 tomically, the lichen thallus very directly reflects 

 the nature of the substratum. A great deal, how- 

 ever, still remains to be done in this direction. 

 The elaborate and careful work of the late Abbe 

 Hue has, unfortunately, not brought much 

 morphological order into our knowledge of lichen 

 structure. 



The whole question of the dependence of one 

 organism, whether animal or plant, on another,, 

 or even others, again whether animal or plant, is 

 every day becoming of greater interest. The 

 views of various lichenologists on this matter are 

 placed before us by Miss Lorrain Smith, but the 

 simple word symbiosis is the term most favoured. 

 It does not define the relationship between alga 

 and fungus in too great a detail. Terms like 

 helotism (due, by the way, to Warming and not to 

 Nienburg), parasitism, consortium, endosapro- 

 phytism, and others, may cover certain individual 

 cases, but the relationship of alga to fungus cer- 

 tainly varies in dift'erent species, or possibly even 

 in different individuals of one species growing 

 under different conditions. There is no doubt 

 that on the whole the lichen-fungus fully controls 

 growth and reproduction of the gonidial algse, 



B 



