2 9 5 
Recent Papers on CEnothera Mutations. 
ploidy in 0. gigas originates from the chance union of two unreduced 
or diploid germ cells. In support of this view these investigators 
announced independently the discovery of triploid or 3x mutants 
having twenty-one chromosomes. Stomps found one such mutant 
from Lamarckiana, which he calls semigigas ; and eleven Hero or 3x 
mutants from Lamarckiana and its mutants rubrinervis and lata 
pollinated by cruciata, muricata, biennis or Millersi. The frequency 
of triploid forms in these crosses (they were easily recognizable by 
their larger size and deep green colour) was about three per 
thousand. But it seems probable that these triploid mutants have all 
originated from the fertilization of a 2x (diploid) egg by a normal 
or haploid pollen grain, especially as in the reciprocal crosses 
triploid forms do not appear to have been found. These crosses do 
not therefore, as Stomps has supposed, furnish evidence of the 
occurrence of diploid pollen-grains. The same is true of the eight 
triploid mutants obtained by Miss Lutz. They may all have come 
from 2x eggs fertilized by pollen-grains having x chromosomes. 
There is, furthermore, no observational evidence of the existence 
of diploid pollen-grains, though the megaspores which have been 
milch less studied have furnished a case (Geerts) of a megaspore 
mother-cell of Lamarckiana having twenty-eight chromosomes. 1 
pointed out (16) the probability that such a cell would develop an 
embryo after omitting both reduction and fertilization, and that 
gigas mutants may therefore originate in this manner. It has also 
been pointed out (20) that the occasional rare pollen-grains of 
Lamarckiana which, like gigas, have four lobes instead of three, may 
be diploid in chromosome-content. But there is at present no 
evidence that such pollen-grains are functional. The exact manner 
of origin of gigas hence remains uncertain, though it is possible that 
both methods of origin may occur. The discovery of triploid 
mutants, however, indicates the sporadic occurrence of diploid eggs 
in Lamarckiana and its derivatives, though there are of course other 
conceivable ways in which triploidy might have originated, such as 
the formation of the embryo from a triple fusion endosperm nucleus. 
This method is improbable, however, for the CEnothera embryo-sac 
only contains four nuclei (two synergids, the egg and a polar 
nucleus) and there is very little endosperm-formation. 
It is highly probable that the exceptional degree of variation in 
gigas is concerned, at least in part, with changes in the chromosome- 
number of different individuals. A number of these types have 
been figured (21, 24). 
Series of mutations which are parallel to those of Lamarckiana 
have been obtained by Stomps (29) and by Gates (18) in different 
races of O. biennis. Stomps obtained two mutants from the F 2 of 
biennis x biennis cruciata. The cruciate variety differs from the 
normal (from which it has probably originated by a mutation) 
only in the cruciate character of the flowers. This character 
behaves as a Mendelian recessive, splitting out in F 2 . In the F 2 
appeared one O. mut. biennis nanella (dwarf), and one O. biennis 
semigigas which was larger and possessed twenty-one chromosomes, 
having also long styles unlike biennis races. 
In a race of O. biennis from the Madrid Botanical Garden, 
which had evidently undergone crossing (18), many of the plants 
belonged to types corresponding to Lamarckiana, rubrinervis and 
