100 THE PEARS OF NEW YORK 
Self-sterility and self-fertility are greatly influenced by the condition 
under which a variety is grown. Thus, a variety is often self-sterile in 
one locality and not in another. Occasionally Bartlett, usually nearly 
or quite self-sterile, and other varieties as well, set fruit one season and 
not the next. All pears, the Bartlett in particular, seem to have a greater 
degree of self-sterility in eastern pear regions than on the Pacific slope. 
In general, the better the adaptation of a variety to its environment the 
better it sets fruit with its own pollen. It is obvious, therefore, that it 
is not possible to give lists of self-sterile and self-fertile varieties. Such 
lists can be made out only for regions and localities. Some varieties, 
however, more often fail to set fruit because of self-sterility than others. 
Among standard pears, Bartlett, Beurré d’Anjou, Beurré Clairgeau, Clapp 
Favorite, Howell, Kieffer, Lawrence, Sheldon, and Winter Nelis appear to 
be most often self-sterile. Beurré Bosc, Flemish Beauty, and Seckel are 
usually self-fertile. 
A self-sterile variety usually sets fruit when another variety is at hand 
to supply pollen. Several considerations determine the selection of varieties 
to interplant. Thus, the two varieties must blossom at the same time if 
cross-pollination is to be effective. The table on pages 88 to 90 shows the 
sorts that bloom at the same time, or nearly enough so to make cross- 
pollination possible. Under normal conditions, the blooming time of 
varieties overlaps sufficiently for cross-pollination excepting those that 
bloom very early and very late. If the table is used for regions much to 
the north or to the south of this Station, allowance must be made for a 
shorter blooming period the farther north; a longer one the farther south. 
That varieties of pears have sexual affinities is another consideration that 
merits some attention. That is, one variety will fertilize another sort 
very well, while pollen from a third may not be at all acceptable. 
“ Affinities ’’ can be determined only by hand crossing. Probably the 
importance of affinities is over-rated. The distance between varieties set 
for cross-pollination must not be too great — not more than two or three 
rows apart. For convenience in harvesting, varieties should be selected in 
relation to ripening. Only commercial varieties should be interplanted, as 
the wastage is too great if comparatively worthless sorts are set to fertilize 
a standard commercial variety. 
Some disadvantages attend the setting of mixed orchards of pears, 
and these must be weighed and overcome as far as possible. There are 
many current statements to the effect that all varieties, whether self-sterile 
