POTATO BREEDING AND SELECTION. 7 
slight tinge of purple. Generally speaking, varieties with pale lemon- 
yellow flowers do not produce pollen freely and as a rule their pollen 
is not viable. 
HAND TECHNIQUE. 
The technique of cross-pollinating potatoes by hand is compara- 
tively simple, but since relatively few of our commercial varieties 
develop viable pollen, the percentage of success is correspondingly 
small. Obviously the first step in the cross-pollination of the potato 
is the selection of the seed-bearing plants. Strong, healthy plants 
should be chosen for this purpose, of a variety possessing certain 
definite characters which it is desirable to combine with certain other 
desirable characters of another plant. 
The next step is the selection and emasculation of the flowers and 
the bagging of the same. The proper stage at which emasculation 
should be performed is shown in Plate II, figure 1. This varies some- 
what with the variety or species. Generally speaking, it should be 
done before the pistil protrudes through the bud, or a day or two in 
advance of the opening of the flower. The only instrument necessary 
for the removal of the stamens is a pair of sharp-pointed forceps. 
The operation is most easily accomplished by clasping the bud by 
the lower portion of the calyx with the forefinger and thumb of the left 
hand and then opening up and pushing back the corolla with a pair 
of sharp-pointed forceps; after this the stamens are easily removed 
by pressing each of them away from the pistil until the filament snaps 
off at its base. Plate I, figure 1, B, shows a potato blossom from which 
the stamens have been removed in this way. It is usually desirable 
to emasculate as many flowers in each cyme as are at the right stage 
of maturity. All the immature buds and mature flowers should be 
removed before inclosing the emasculated flowers in a paper bag 
(PI. II, fig. 2). A 1-pound bag — that is, a paper sack having the 
capacity mark of 1 pound — is large enough for this purpose. To facili- 
tate the work of putting on the bags, it has been found convenient to 
punch holes through the sides of the bags and to draw strings through 
these holes prior to going to the field (PL III, fig. 1). It has also 
been found desirable to inclose in the bag the young shoot bearing 
the flower cyme, or, where this is not feasible, to include as much 
foliage as possible around the flowers. 
The flowers are usually ready for pollinating one to two days after 
emasculation, depending upon the stage of maturity when emascu- 
lated and upon the character of the weather subsequent thereto. 
During the first few years in which the writer was engaged in potato 
breeding, various methods of removing the pollen from the anthers 
were practiced. One method was that of collecting in the early 
morning flowers from plants selected as pollen parents and bringing 
