A DOMINANT MENDELIAN CHARACTER. 305 
The Appearance of Male Sterility in Fertile Lines. 
So far we have dealt with “ presence " or * absence ” of pollen as the main 
feature of male sterility. In the following is evidence of the sudden appearance 
of sterility due to the “quality” of the pollen and only partially associated 
with “absence” of pollen, and not at all with deformity of the anther. 
The variety known as Sutton's Flourball, which has been extensively 
used in my potato experiments, is a red-skinned variety which flowers freely, 
sels seed readily, and has abundant pollen of a high quality. In 1906 a 
flower of this variety was selfed, producing 200 seedlings, and from one of 
the white-tubered seedlings, viz. D 1907, which arose from it in 1907, а selfed 
fruit was obtained ; this contained only about a dozen seeds, and only five of 
these seeds germinated, of which two bore tubers, viz. D! 1908 and D? 1908. 
In 1909 both D! and D? were grown and were fairly vigorous plants 
flowering freely, but they possessed only a medium quantity of pollen, and 
that entirely dead. Repeated endeavours failed to self-fertilize flowers of 
either of these two plants. 
D 1907 was grown on in 1908, and a selfed ball obtained which contained 
only ten seed, of which only four germinated, and although every effort was 
made to keep and protect these seedlings they failed to flower. 
D 1907, grown again in 1909, produced after many efforts at fertilization 
two seed-balls, but they contain relatively few and rather immature-looking 
seed. 
A similar tendency to become sterile on the male side was found in another 
line “G” isolated from Sutton’s Flourball. In 1907, 150 seedlings were 
raised, and one of these selfed, giving in 1908 seven seedlings : two were 
white, five red tubers. The red-tubered plants in 1909 bore flowers with 
abundant and good quality pollen ; the white-tubered ones, G! and G?, bore 
also abundant flowers and were self-fertilized many times, but their pollen 
though fair in quantity was very bad in quality, and only one seed-ball, 
which, however, contained a good member of immature seed, was obtained 
from СИ. G? bore no fruit. In 1910, families of seedlings were raised both 
from G? and G^, red-tubered plants, and in both there were many individuals 
who possessed but very poor pollen, 2, e. it was mostly dead, whilst in a few 
there was no pollen formed. Deformity, however, was not observed in any 
of the anthers. 
If Table IV. of pollen examinations be now studied, 16 will be seen how 
variable the pollen is in these two lines D and G, and what a strong tendency 
there is towards the formation of “round” pollen in the dry state, a fact 
whieh I think undoubtedly points to some condition inhibiting the manu- 
facture of perfect pollen. 
In both D and G we have two lines starting as highly fertile, and, in both, 
plants arise which have a tendency towards the production of sterile pollen, 
