152 Notes on Recent Literature. 
symmetrically during the cell divisions, in such a way that each cell 
has received a complete series of pangens. But this method of 
symmetrical distribution is replaced by a new plan of symmetry in 
the formation of the germ-cells, such that, to take the case of a 
simple di-hybrid in which segregation is complete, one half of the 
germ-cells are of one kind, the other half of another kind, and each 
kind is pure in respect of the character which it bears. As Bateson 1 
has said, this symmetrical arrangement can only be regarded as a 
consequence of some numerical symmetry in the cell-divisions of 
gametogenesis. But the symmetry is of a different kind from that 
which extends over the somatic cells; the change of symmetry 
which cytological studies have shown to occur in the heterotype 
division is just such an one as is required to meet the case, and it 
occurs, in all probability universally, wherever sexual reproduction 
occurs. In spite of all the difficulties of directly identifying the 
nucleus as the carrier of inherited characters, it is hard to 
believe that such a parallel can b^ a mere coincidence, and without 
significance in the distribution of the characters to the gametes. 
But whatever weight may be attached to such a parallel as 
this, it amounts at the best to nothing more than a presumption ; 
what is required to substantiate modern views on the significance 
of the heterotype division, is evidence which will definitely connect 
the nucleus with the transmission of inherited characters. Until 
that has been provided much that has been written and said, more 
especially with regard to the details of the hypotheses, belongs 
to the realms of pure speculation. The cytological study of pure 
races and hybrids, which show partial or total sterility, 2 has 
scarcely realized the hopes which were entertained of acquiring 
direct evidence. In the majority of such cases the sterility cannot 
be referred directly to abnormalities occurring in the nucleus itself, 
either in the condition of rest or of division. A very hopeful field 
however is opened out by the study of races in which new types are 
being thrown off, as in the species of Oenothera, which have been 
examined by Gates, 3 Miss Lutz 4 andGeerts. 5 Gateshasfoundthatthe 
pairing between the chromosomes in the heterotype division does 
not always take place ; this allows irregularities in the distribution 
1 Brit. Ass. Rep., 1904, p. 583. 
2 A general review of this subject has recently been given by 
Tischler in the Arch. Zellforscli., 1, 1908, pp. 33-151. 
3 (a) “ Pollen development in hybrids of Oenothera lata and O. 
Lamarchiana." Bot. Gaz., 43, 1907, p. 81. 
(b) “ Hybridization and Germ-Cells of Oenothera mutants.” 
Ibid. 44, 1907, p. 1. 
(c) “ The Chromosomes of Oenothera." Science, N.S. XXVII., 
1908, p. 193. 
(d) “ A Study of Reduction in Oenothera rubrinervis." Bot. Gaz., 
46, 1908, p. 1. 
4 “ Chromosomes of the Somatic Cells of the Oenotheras." 
Science, N.S. XXVII., 1908, p. 335. 
6 (a) u Ueberdie Zahl der Chromosomen von Oenothera Lamarchiana." 
Ber. d. D. Bot. Ges., 25, 1907, p. 191. 
(b) “ Beitrage zur Keeintniss der cytologische Entwicklung von 
Oenothera Lamarchiana." Ibid, 26a, 1908, p. 608. 
