POTATO BREEDING AND SELECTION. 11 
RESULTS OF EXPERIMENTAL CROSSING. 
Although many crosses wore made by the Writer prior to 1909, the 
results secured Were of such a meager nature as to be unworthy of 
mention. In 1909, however, so many successful crosses were made 
as to cause the writer to inquire the reason thereof. This inquiry 
he has been unable to answer more satisfactorily than to suggest that 
it may have been due to more favorable growing conditions at the 
time the plants were developing buds and flowers, thus furnishing 
the right conditions for the development of viable pollen. 
One of the main objects of the 1909 experiments was to secure as 
many crosses as possible between the disease-resistant German varie- 
ties and those American varieties which would cross with them. 
The anxiety to succeed was perhaps responsible for the use of a few 
undesirable pollen parents, which always afforded an abundance of 
viable pollen and could therefore be depended upon to effect a cross 
when all other sources failed. The abundant results secured served 
to convince the writer of two facts which had previously been rather 
puzzling: (1) It demonstrated conclusively that the ovaries and 
pistils of many of the varieties in the collection were normally devel- 
oped and that lack of success was not due to this cause, and (2) it 
emphasized the necessity of paying greater attention to all varieties 
which produce viable pollen, as well as to those which produce it 
sparingly or not at all. A further observation was also made with 
respect to the secretion of stigmatic fluid by the glands of the stigma. 
Practically every writer who has had occasion to describe the potato 
flower in connection with the subject of plant breeding has told his 
readers that the stigma is in a receptive condition when it is covered 
with a fluid secretion. .This condition of the stigma has rarely been 
observed and then only when the pistil has passed beyond the stage 
of successful fertilization. It is doubtful whether the secretion of a 
stigmatic fluid is a normal function of the potato blossom at the 
present time. 
The accompanying record of the 1909 crosses, which is presented as 
Table I, gives the parentage, number of flowers crossed, number of 
seed balls developed, percentage of success, and the number of seed- 
lings that produced tubers. 
A study of Table I discloses some rather interesting data, partic- 
ularly with respect to the behavior of seed-bearing plants when pol- 
linated with different varieties. In the first cross recorded, Geheimrat 
Theil X Keeper, six flowers were pollinated and five seed balls were 
developed, from which 502 tuber-bearing plants were produced. 
The same variety when mated with XX Early developed only one seed 
ball from 11 pollinated flowers, and this did not produce a single 
tuber-bearing plant. When crossed with Solanum maglia, a wild 
South American species, it failed to set fruit, and the same negative 
