- 23 - 
1927. Factors influencing the yield of apples in the Cumberland- 
Shenandoah region of Pennsylvania, Virginia, West Virginia. 
U. S. Dept. Agr. Tech. Bui. 54, 25 po. 
p. 21: A number of growers attributed low yields to failure 
of fruit to set. It was commonly observed that the low yields of 
the Winesap and varieties of the Winesap family were ascribed to 
this factor. These varieties are largely self-sterile and must be 
cross-pollinated by some other variety. Self-sterile varieties 
should not be planted in solid blocks or isolated from other orchards. 
Where self-sterile varieties have been so planted the results may be 
improved by top-working every fourth or fifth tree in every fourth 
or fifth row with some variety that is a good cross-pollinizer. Bees 
are essential in any orchard and are effective in securing pollina- 
tion even during cold, wet seasons . 
Avocado 
Stout, A. B. 
1933. The pollination of avocados. Fla. Agr. Expt. Sta. Bui. 257, 
44 pp. 
p. 42: It is without doubt advisable (1) to interplant 
avocados on the basis of their flower behavior (2) to supply bees 
in abundance to effect pollination . 
Traub, H. P., Pomeroy, C. 3., Robinson, T. R., and Aldrich, W. W. 
1941. Avocado production in the United States. U. S. Dept. Agr. Cir. 
620, 20 pp. 
p. 3: With some varieties, as Fuerte, there is sufficient 
overlap of the two sets of flowers to render them self-fertile; with 
other varieties, a sufficient percentage of single-cycle flowers 
(completing their anthesis in one opening) are produced to render 
self-pollination easy of accomplishment, the only requirement in 
each case being the activity of bees or other insects ... . 
Keeping bees in or about the orchard is also considered a 
wise provision during the blooming period. Observations indicate 
that pollen is carried considerable distances by bees and doubtless 
by other flying insects. 
Blackberry 
Darrow, G, M. 
1937. Blackberry and raspberry improvement. U. S. Dept. Agr. Year- 
book 1937: 496-533. 
p. 498: Normally the wild blackberries of the East are entirely 
