Self-sterility in Dewberries and Blackberries 
17 
sterile, notwithstanding the fact that its flowers frequently have an 
excessive number of petals. 
If we carefully examine the flowers of our cultivated varieties of 
dewberries and hybrid blackberries we notice that two varieties, viz., 
Premo and Rathbun, show irregularities in the formation of their 
stamens. The flower buds of Premo are different from those of most 
other varieties of dewberries and blackberries in that the pistils rapidly 
elongate and protrude from the flower buds several days before the 
Fig. 4. —Flower clusters of Premo (dewberry), showing liow the pistils protrude from 
the bursting flower buds. 
petals expand, and before the stamens mature. This apparently is a 
provision for securing cross-pollination. 
Also, very often the stamens of the flowers are defective. Many of 
them never develop beyond mere rudimentary organs, some partly de¬ 
velop, others have their filaments dwarfed, and still others develop 
normal filaments but with anther sacks that are diseased and which 
liberate only defective or aborted pollen. The remaining stamens ap¬ 
parently produce normal pollen, hut fruit will not set when the flowers 
are self-pollinated. 
