October 20, 1898J 



NATURE 



591 



pits, cellars, &c., assumes very grotesque forms in which 

 the pileus is suppressed, and the stems consequently 

 more or less resemble species of Clavaria, but hitherto 

 every one considered these productions simply as mon- 

 strosities due to an exceptional environment. Whether 

 these antiquated views, or the later one propounded by 

 Dr. Holtermann prove to be correct, we consider yet 

 remains to be proved. 



Polyporus polyinorphous, as found in nature, resembles 

 a bracket in form attached by one edge to the matrix, 

 from which it projects at right angles. The spores of 

 this species in cultures produce a thin crust attached by 

 its entire under surface to the substratum, its upper 

 surface being covered with pores bearing the hymenium, 

 a Porta in fact. In this case again, systematists have 

 long known that the higher forms included under 

 Polyporus, Fames, and Polysticttis, not unfrequently 

 develop the resupinate or Porta form, often showing 

 every transition from one to the other ; but this was 

 included under the presumed elasticity of the species, as 

 such forms are developed move especially when the 

 fungus occurs in conditions different from those under 

 which it appears in its normal or highest known stage 

 of development. Every departure from the normal form 

 of a species cannot surely be considered as a retro- 

 gression towards a phase lower in the evolution of the 

 species, even if the exceptional development bears a 

 resemblance to some genus lower in the scale of organ- 

 isation, and through which phase the species under 

 consideration may presumably be supposed to have 

 passed. Pure cultures in various nutritive media grown 

 on a slip of glass come under the category of things 

 grown under conditions that may be termed as ex- 

 ceptional, to say the least, and the fact that such 

 developments represent phases in the normal life-history 

 of the species investigated, or indicate its phylogeny, 

 has yet to be proved. 



Another new genus is named Vajt Romburghia, the 

 one species stands as V. R. silvesiris. 



In the introduction the author states that as his 

 principal object is to elucidate the life-history of forms, 

 he has not attempted pedantic diagnoses of forms. 

 Having been sufficiently pedantic to establish five new 

 genera, and above a score of new species, the amount of 

 pedantry would not have been much accentuated by the 

 addition of diagnoses of each of these. Apart from 

 interpretations bearing on the cultures, every mycologist 

 will welcome the work done by Dr. Holtermann, which 

 is a model of exactness, and bears on its face the stamp 

 of accuracy. The twelve plates add much to the value 

 of the work. G. Massee. 



OUR BOOK SHELF. 



Applied Magnetism : an Introduction to the Design of 

 Electroiiuii^netic Apparatus. By J. A. Kingdon, B.A. 

 Pp.292. (London: H. Alabaster, Gatehouse, and Cp.j 

 Mr, KiNciDON commences his book with the magnetic 

 flux, and his readers are evidently expected to bring their 

 equipment of dynamics, elementary information as to 

 units and electrical phenomena, with them. Ohm's law 

 is introduced apparently for the purpose of bringing in its 

 magnetic equivalent, and the fact that the coincidence is 



NO. 15 12, VOL. 58] 



rather one of form than substance ought, we think, to 

 have been pointed out. Reluctance and permeability 

 are defined and shortly treated, and tables of magnetic 

 force, induction, and permeability are given for various 

 kinds of iron. Then follow specimens of elementary 

 calculations regarding magnetic circuits. 



The next chapter is entitled Magneto-motive Force of 

 Current. The magnetic fields of different simple arrange- 

 ments of conductors are first discussed, thus the force at 

 the centre of a circular coil is worked out, and the field 

 intensity — Biot and Savart's result — for a straight cur- 

 rent is calculated from the simple law of magnetic force 

 due to an element of a current. This law, as a matter of 

 fact, was derived by Laplace from Biot and Savart's 

 result for a straight current, and the recovery of the ex 

 perimental result is interesting only as showing how the 

 inverse square of the distance law for an element leads to 

 the law of the inverse distance for a long straight con- 

 ductor. The exact directions of the magnetic forces 

 produced by the currents in elements of conductors seem 

 not to be always quite clearly given, and some amplifica- 

 tion of this part of the book seems desirable. We may 

 say that we do not like the name " mags " any more than 

 we liked the names " hens " and " millihens," which were 

 once proposed for other units. Abbreviations which have 

 any flavour of extraneous association should not be 

 tolerated. 



We come next to Tractive Force of Magnets and 

 Current Reactions, with the pereameter method of testing 

 iron, and some results thereby obtained for Krupp steel 

 and Lowmoor iron. 



Next we have a rapid account of the Generation of 

 Electromotive Force by variation of magnetic flux through 

 a circuit, or across a moving conductor, and the idea of 

 self-induction is introduced. What exactly the self- 

 induction or self-inductance of a coil is does not seem to 

 be defined, though several things have their definitions 

 given which certainly do not more deserve attention. 



Alternators and other forms of direct current generator 

 are described, and specimens of various calculations 

 given. But we have looked in vain for the characteristic 

 curves by which Hopkinson did so much for the practical 

 working out of the dynamo. Surely in a book the object 

 of which is to deal with practical calculations regarding 

 magnetic circuits, this matter of all others ought to have 

 received attention. Yet it is not even mentioned 1 



The book will be found to give information of 

 considerable service on many points, but it is not 

 homogeneous and consistent enough in its treatment. 

 The chances are about even that if it is consulted on 

 some important point the matter vvill not be found treated. 

 With some rewriting and additions its usefulness will 

 be much increased. 



Biomechanik erschlossen aus dem Principe der Organ- 



ogenese. By Dr. E. Mehnert. Pp. viii -f- 177. (Jena: 



Fischer, 1898.) 

 At a time when " vitalism " is rife, and the disbelief in 

 Natural Selection is almost a disease, an attempt to ex- 

 plain the phenomena of development on mechanical 

 grounds is very welcome. 



In this treatise Mehnert has examined very thoroughly 

 the groundwork of organogeny, and has had little diffi- 

 culty in showing, by reference to the development of such 

 organs as the heart and blood-vessels, the pineal eye, the 

 neurenteric canal, and so on, that the exceedingly loose 

 interpretation commonly given to the law of recapitulation, 

 namely that embryogeny is, pure and simple, a repetition 

 of phylogeny, is absolutely incorrect ; in fact, the onto- 

 genetic is frequently the very reverse of the phylogenetic 

 order — in all cases the order of development has become 

 changed. 



By a careful consideration of very numerous facts 

 Mehnert shows that the principal factors in this alter- 



