620 



SCIENCE. 



[N. S. Vol. XXIV. No. 620. 



understood by such persons, at least with 

 readiness. 



Eighteen pages are devoted to vegetative 

 reproduction with a discussion of cuttings, 

 runners, bulbs, tubers, grafting, etc., in the 

 higher plants, and of conidia, swarm-spores 

 and fission in the fungi and algae. Eighty- 

 seven pages treat of sexual reproduction. The 

 author traces the history of the knowledge of 

 sexuality in plants from the Greek philos- 

 ophers down to its demonstration by Camer- 

 arius, confirmation by Kohlreuter, discovery 

 of the pollen-tube by Amici, observation of 

 sexuality in cryptogams by Hofmeister, Thu- 

 ret and Pringsheim, and the more recent in- 

 vestigations showing the part played by the 

 nuclei, chromosomes, synapsis, etc., thus bring- 

 ing the subject down to this year. After this 

 historical and general discussion the different 

 groups of plants are taken up, showing the 

 increasing complexity of the sexual process 

 from the union of two equal cells up to the 

 complicated processes in the higher fungi and 

 algse, the alternation of generation and devel- 

 opment of heterospory in the Archegoniatse 

 and the double fertilization in the Angio- 

 sperms. Under the caption General Questions 

 are taken up sexual affinity, hybrids, poly- 

 spermy, parthenogenesis, parthenocarpy, apo- 

 gamy, apospory, merogony and determination 

 of sex. The final considerations take up the 

 theory of fertilization and the theory of sex, 

 the various views being presented in an un- 

 biased manner as well as the objections to 

 them. 



Although professedly designed for those who 

 are not specialists this book should prove val- 

 uable for both students and teachers. The 

 references to literature, both old and very 

 recent, although with no pretence to complete- 

 ness, yet give the most important contribu- 

 tions bearing on the subject. The figures are, 

 for the most part, very good. 



Ernst A. Bessey. 



Db. Alfred C. Haddon, F.R.S., University Lec- 

 turer in Ethnology, Cambridge, Eng. : ' The Decor- 

 ative Art of British New Guinea.' (Illustrated.) 



Db. John W. Haeshbeeqeb : ' A Grass-killing 

 Slime Mould.' 



SOCIETIES AND ACADEMIES. 

 THE AMERICAN PHILOSOPHICAL SOCIETY. 



A STATED meeting was held on Friday even- 

 ing, November 2, 1906, at 8 o'clock. The fol- 

 lowing papers were read : 



DISCUSSION AND CORRESPONDENCE. 



SOME POINTS IN TEACHING CRYSTALLOGRAPHY. 



The writer wishes to call attention to and 

 invite discussion of the following points in 

 the teaching of crystallography as a part of 

 the work in elementary mineralogy. 



The best classification even for beginning 

 students is that of the thirty-two crystal 

 classes, based upon symmetry. All ideas of 

 hemihedrism should be dropped as there is no 

 structural connection between the whole and 

 partial forms. The name of the class is the 

 name of the general form. Groth's set of 

 names is the best, but his names for the iso- 

 metric classes may be replaced by the terms, 

 tetartoidal, gyroidal, diploidal, hextetrahedral 

 and hexoctahedral for classes twenty-eight to 

 thirty-two. 



A division of crystals into seven systems is 

 preferable to that of six. Crystals with an 

 axis of three-fold symmetry naturally form 

 one system and those with an axis of six-fold 

 symmetry another system. And this is true 

 whether the three axes of Miller or the four 

 axes of Bravais are used. The writer prefers 

 to treat the orthorhombic system, one of 

 moderate symmetry, first. 



It is believed that von Fedorow's method of 

 naming forms (adopted by Groth in his 

 ' Physikalische Kristallographie ') is the only 

 logical one. The name of a form depends 

 upon its shape and is independent of how it 

 cuts the axes of reference. A pinacoid consists 

 of two parallel faces whether its symbol is 100, 

 hOl, hJcl or what not. A pyramid is three or 

 more like faces meeting in a point and a bi- 

 pyramid is two such solids placed base to base. 

 Instead of using a name for the particular 

 form, e. g., pinacoid of the first kind, as von 

 Fedorow does, we may simply give the name 

 of the form together with the symbol, e. g., 

 pinacoid (100). 



