1909] CURRENT LITERATURE ; 469 
heterozygous state. EMERSON concludes that there are two distinct and unrelated 
units for mottling, one of which is a typical Mendelian dominant, the other 
becoming evident only in the heterozygous state, and on this basis he works out 
the expectation of various types of crosses. It remains to be demonstrated by 
actual breeding that such peculiar ratios may exist as 11:5, 21:38, 33:15, 16, etc. 
A number of more or less popular expositions of Mendelism have appeared, 
and it is not necessary to mention these except in case new scientific matter has 
been used by way of illustration. One of the best of these general discussions 
is that of BAur,"4 in which the illustrative material is almost entirely derived from 
his own experiments with Antirrhinum majus. In this species 15 or more differ- 
ent hereditary units have been demonstrated, and the author inclines to the view 
that much of so-called fluctuating variation is really Mendelian splitting of less 
prominent unit characters. The number of demonstrated units in this species 
exceeds the number of chromosomes, which leads the author to the conclusion 
that whole chromosomes cannot be the units upon which these characters depend. 
AUR adheres strictly to the presence and absence hypothesis. SPILLMAN,'S 
in a review of Baur’s paper, shows that so far as yet demonstrated the individual 
chromosomes may be the fundamental bases of these unit characters, although 
several instances are known in which the number of demonstrated unit characters 
in a species is in excess of the known number of chromosomes. The crucial 
test must be the finding of an individual having more independent characters 
than sy has chromosomes. This has not yet been done. 
6 has once again repeated one of MENDEL’s original experiments 
in order to determine whether there is any influence of pre-parental ancestry upon 
the offspring, a question involving the essential difference between the Mendelian 
and Galtonian conceptions of heredity. It was well that this experiment should 
be undertaken by one who was in the beginning a staunch Galtonian. The 
result of the t leads DARBISHIRE to the conclusion that ‘‘there is nothing 
like ancestral cuatiation within the limits of a single unit character,” or in 
other words that segregation is perfect and the recessive character appears in as 
large a proportion of the offspring of a heterozygote after six generations of selec- 
tion to the dominant character as in the F,. 
The Mendelian theory of heredity has produced a very deep impress upon 
the practical work of plant and animal breeding, and a considerable number of 
papers have appeared from economic sources which present valuable a Olly 
data in support of this theory, and indicating the extent of its applicability. 
a few of the more important of these papers can be noted here. Besides the sade 
™4Baur, E., Einige Ergebnisse der experimentellen Vererbungslehre. Beih. 
medizinischen Klinik 4: 265-292. 1908. 
»sSprttman, W. J., The nature of “unit” characters. Amer. Nat. 43:243-248. 
T909. 
6DarpisHire, A. D., An experimental estimation of the theory of ancestral 
contributions in heredity. Proc. Roy. Soc. London B 81:61-79- 1999- 
