RECENT ADVANCES IN SCIENCE 197 



In a discussion with A. E. H. Tutton (Journ. Wash. Acad. 

 Sci., 9, 94, 1 91 9), E. T. Wherry {ibid., 8, 840, 191 8 ; 9, 94, 

 191 9) maintains that the symmetry of the " crystal-molecule " 

 (the unit of the lattice) must be considered as well as the sym- 

 metry of the lattice as a whole in determining the crystal class, 

 and that crystals may belong to different classes according to 

 the basis which is adopted. Tutton controverts the statement 

 that on the basis of one property a crystal may belong to one 

 class, and on the basis of another, to another class. 



In the past year the structure of a number of crystals has 

 been determined. A. J. Bijl and N. H. Kolkmeijer {Chem. 

 Weekbl., 15, 1264, 191 8 ; Proc. Akad. Amsterdam, 21, 405, 494, 

 501, 1 919) have investigated the structure of white and grey tin. 

 The former is regarded as divalent and tetragonal, and the latter 

 as tetravalent and octahedral. C. L. Burdick and E. A. Owen 

 {Journ. Amer. Chem. Soc., 40, 1749, 191 8) find carborundum to 

 be composed of two interpenetrating face-centred rhombohedral 

 lattices, the angle being almost 90 degrees, and each being 

 displaced along the hexagonal axis a distance equal to 0-36 of 

 the basal edge (cf. T. V. Barker, loc. cit.). This structure is 

 similar to that of the diamond if half of the carbon atoms be 

 assumed to be replaced by silicon, which, however, are not in 

 the centre of the carbon tetrahedra. A. W. Hull {Phys. Rev., 13, 

 292, 1919), on the other hand, maintains the exact equivalence 

 of the diamond and carborundum structures. 



By a modification of Debye's method, H. Bohlen {Ann. 

 Phys. [4], 61, 421, 1920) finds thorium and nickel to be composed 

 of face-centred cube lattices, and magnesium of two interpene- 

 trating simple hexagonal lattices. According to P. Scherrer 

 {Phys. Zeit., 19, 23, 191 8), aluminium is similar to copper, etc., 

 and has a face-centred lattice whose edge measures 4-07 X 10"* 

 cm. F. Rinne {Cent. Min., 129, 1919) has determined nephe- 

 line to belong to the hexagonal pyramidal class, and ice {Ber. 

 Sachs. Ges. Wiss., 69, 57, 191 7 ; Neues Jahrb. Min., 25, 1919) 

 to the dihexagonal bipyramidal class, the structure resembling 

 that of magnesium (cf. Cent. Min., 137, 191 8). 



BOTANY. By E. J. Salisbury, D.Sc, F.L.S., University College, London. 

 Phytogeny and Morphology. — Several of the papers, read at the 

 joint session of American Botanists at St. Louis in December 

 last, dealing with the Phylogeny of Seed Plants, have recently 

 appeared in the Amer. Jour. Bot. Bucholz reviews the 

 details of the embryology of the Coniferse and emphasises their 

 phylogenetic importance. Pifius is regarded as very primi- 

 tive in this respect, stress being laid upon its cleavage poly- 

 embryony, with eight potential embryos derived from the four 

 initials and the four rosette cells. The development of a cap 



