16 BULLETIN 195, U. S. DEPARTMENT OF AGRICULTURE. 
from which 10 plants were obtained. It is evident from these fig- 
ures that the pollen of Keeper was much more potent than that of 
Venezuela. 
VARIETAL AFFINITY. 
It is apparent to those familiar with plant breeding that certain 
types or strains of a given class of plants possess greater sexual affinity 
for each other than do other types or strains which are apparently 
as closely related. This phenomenon has been observed by potato 
breeders and has been taken advantage of in making crosses. One 
of the most interesting observations upon this point that has come 
to the writer's attention is that made by Taylor/ who says: 
Careful experiments this season with that fine potato named Factor have proved 
that it is not only sterile to its own pollen, but also sterile to all the Up-to-Date type, 
of which class Factor is probably the best example. ... It will cross with some 
of the colored-skinned varieties, which have also flowers of a similar tint, but the 
seed vessels mature very slowly and never attain a large size. Where pollen of 
white-flowered sorts can be obtained, such as the Admiral, Provost, Abundance, and 
Cumberland Ideal, a good set can be obtained on Factor and the pods soon attain 
full size; indeed, the growth of the so-called "plum" is remarkable in comparison 
with that of the others already noted . . . the pollen of Factor has been found to be 
absolutely sterile to some 30 other varieties of potatoes having flowers and tubers of 
different colors and none of them of the Up-to-Date class. 
In this connection, Findlay 2 says of the Up-to-Date potato: 
Its organs of reproduction are 90 per cent of them malformed. The stamens or 
pollen cases are small and never, so far as I have seen, contain one grain of pollen. 
The pistil is also of the same character. . . . the Up-to-Date potato beat me off 
so far as being able to effect my purpose, compelling me to fall back, as a last resource, 
on its male parent, or rather a natural seedling from the same. I then effected my 
object, and got two or three plums. But, as showing how much the Up-to-Date was 
off this job of seed production, the plums were small, containing few seeds, and of 
these few only about 53 per cent germinated. 
The following data obtained from crosses made in 1909 seem to 
fully corroborate the observations made by Findlay with respect to 
the poor seed-bearing qualities of the Up-to-Date (Table I). From 
155 hand-pollinated flowers of this variety, only 23 seed balls were 
secured, and one of this number was found to be seedless. The 
seeds secured from the 22 successful crosses produced only 671 
tuber-bearing seedlings, or an average of a little over 30.5 tuber- 
bearing plants per berry. Seven pollen parents were used in mak- 
ing the crosses, and three of these, the Norcross, Empire State, and 
Fuerst Bismarck, did not produce a single seed ball. These are 
varieties that produce pollen very sparingly or not at all. Successful 
crosses were secured with Keeper, Early Silverskin, Irish Seedling, 
and Round Pinkeye, all of which produce pollen abundantly. The 
Irish Seedling gave the highest percentage of successful crosses 
(41.2 per cent), but for some reason produced a woefully small 
i Taylor, G. M. The cross fertilization of the potato. In Gard. Chron., v. 48, 3d ser., 1910, p. 279. 
2 Findlay, A. The potato: Its history and culture. In North British Agriculturist, Jan. 25, 1905, p. 17. 
