1915] CURRENT LITERATURE 165 
went division. This is the first step in true parthenogenesis, but it is never 
a oat by cell division and never leads to embryo formation. Other 
orks on apogamy are cited, but the author believes the cytological facts 
ons such matters are yet too few to warrant the formulation of a hypothe- 
sis on the evolution of parthenogenesis from amphimixis. 
e value of contributions of this sort is obvious. The correlation of 
physiological conditions and morphological phenomena is clearly shown. 
This should lessen the morphologist’s frequent neglect of physiology, an 
on the other hand, should lead to a more careful checking up of bxcedeodnbil 
results, especially those in plant breeding, by morphological study.—L. W 
SHARP 
Chromosomes and Mendelian inheritance. Reign. iw iea:§ presents a 
recapitulation with much new data bearing upon the “‘couplin, 
mn the chromo eA 
pretation of Mendelian phenomena. e large number of ‘‘cross-overs”’ (that 
is, changes from coupling to repulsion and vice versa between two given genes) 
and the relatively small number of chromosomes in the fruit fly, makes this 
organism very favorable material for such a study. Over 40 Mendelian char- 
among the same series of “linked” genes may be teary calcu 
gene is assumed to occupy a definite position or “locus’’ in the sey 
and these loci are represented as forming a linear series ie distances from 
one another is measured by the relative frequency of cross-over. When cross- 
overs between two genes are rare, the two loci involved are assumed to be very 
near each other, and when cross-overs are frequent it is assumed that the two 
loci in question are correspondingly removed, though still lying in the same 
chromosome. No less than six of these loci have been established in a single 
chromosome, by a fairly adequate amount of data, and the correspondence 
between calculated distances and the observed numbers of cross-overs is con- 
vincing as to the fundamental value of this method of representation. Further- 
more, the discrepancies between the observed and calculated results are so 
consistently in the same direction that they make possible another important 
5 STURTEVANT, A. The behavior of the pogo a as studied through 
linkage. Zeitschr. Ind. aes Vererb. 13:234-266. 1915. 
