588 TRANSACTIONS OF SECTION K. 
quent generations; the hybrid AAaa will give, on an average, one pure recessive 
in every sixteen of its offspring; while the hybrid Aaaa will, like the diploid 
hybrid Aa, give one pure recessive in every four plants. 
Ratios of the form 15D: 1R, such as are obtained from the hybrid 
AAaa, recall those obtained in respect of certain characters by Nilsson- 
Ehle* in oats and wheat, and by East* in maize, but in the tetraploid Primulas 
the reduplication affects not merely the factors for isolated characters, but 
extends simultaneously to all the characters which have been studied. The 
numerical consequences of the reduplication of the factors are most conveniently 
studied in cases in which a single dose of the factor is sufficient for the develop- 
ment of the character, because one thus avoids difficulties of classification intro- 
duced by the occurrence of intermediate forms; characters which fulfil this 
condition in the giant Primulas are those of (a) thrum-eye or short-style, as 
contrasted with pin-eye or long-style, and (b) green-stigma, as contrasted with 
red stigma. Crosses between various plants having thrum-eye green-stigma and 
others having pin-eye red-stigma have given the two kinds of hybrid, TTttGGgg 
and TtttGGgg,* which have been identified by their progeny. The former gives 
an F2 ratio of 15D: 1R in respect of each character; the latter gives 3T : 1t and 
15G: 1g. When the hybrids, instead of being self-fertilised, are crossed with the 
recessive, the type TTttGGgg gives offspring in the ratio 3D : 1R in respect of 
each character; while the hybrid TtttGGgg gives equality of thrum-eye and pin- 
eye and 3G:1g. If the two characters are considered together, a hybrid of the 
type TtttGGgg would, in the absence of- special inter-relations between the 
factors, give the curious F2 ratio 45TG : 8T'g: 15tG : 1tg; in the case under dis- 
cussion, however, the results obtained indicate that a complication may be intro- 
duced by the existence of coupling between the factors for thrum-eye and green- 
stigma and further experiment is needed for their elucidation. 
Other characters have been studied, in respect of which the hybrid is more 
or less intermediate between the two pure types. In the case of one character, 
namely, the palmate-leaf as contrasted with the ‘ fern-leaf,’ dominance is com- 
plete in the diploid races, the hybrid, Pp, being indistinguishable in appearance 
from the pure palmate type, PP; but in the tetraploid races a series of curious 
intermediates has been obtained, which are probably of the constitution Pppp. 
In other cases where the diploid hybrid is intermediate, the corresponding form 
occurs among the tetraploid hybrids, but, in addition, there also occur peculiar 
intermediate forms, which are confined to the tetraploid races and are quite dis- 
tinct from the diploid hybrid form. In the case of the factor which, in the 
homozygous condition, inhibits the production of colour in the petals, the tetra- 
ploid hybrid, liii, might, so far as appearances go, very well be classed as a 
coloured form; yet this ostensible recessive is capable of throwing the ‘ dominant 
white.’ 
The results so far obtained do not throw direct light on the problem of the 
possible relationships between factors and chromosomes. The fact that the 
reduplication of the chromosomes has been accompanied by a reduplication of 
the series of factors may, at first sight, suggest a close relation between the 
chromosomes and the factors; but, on the other hand, the tetraploid number of 
chromosomes may be nothing more than an index of the quadruple nature of the 
cell as a whole. There are, however, grounds for hoping that the further study 
of the genetics of the tetraploid plants, especially with reference to the special 
inter-relations between certain factors of which indications have been observed, 
may yield results having a direct bearing in connection with this problem. 
* “Kreuzungsuntersuchungen an Hafer und Weizen,’ I. and II. Lunds 
Univ. Arsskrift, 1909 and 1911; Berichte d. Deutschen Bot. Gesellschaft, xxix., 
1911, p. 65. 
* American Naturalist, xliv., 1910, p. 65. 
* The hybrid type having three doses of either factor, TTTt or GGQGg, is not 
produced by the mating of a dominant with a pure recessive, tttt or gage. It 
can only be formed by the mating of plants producing gametes TT (or GG) 
and Tt (or Gg). 
