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-poUinating 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 fh'st 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 certam 

 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 mstrument necessary 

 for the removal of the stamens is a pair of sharp-pomted forceps. 

 The operation is most easily accomphshed 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 bo 

 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 (PI. Ill, 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 

 emusr-ulation, d('p<!ndiTig Ti])on the stage of maturity wlum emascu- 

 lated and ui>on the cliaracter of tlio weather subsequent thereto. 



During the first few years in which the writer was engaged in potato 

 brer-ding, various metliods of rc^moving th<^ ])<)II('ji from the anthers 

 were jmicticcd. ()n(! method was that of collecting iji tlie early 

 morning flowers from plants selected as jxjJIcn pun'rits uiid l)ringiiig 



