Self-sterility in Dewberries and Blackberries 
33 
many varieties, wliicli are intended to cover the whole fruiting season, 
it is necessary only to have the blooming period of some varieties 
overlap at all times, so that at no time in the booming season should we 
find but one variety in flower. 
From the above table we learn that all of the earliest blooming dew¬ 
berries belong to the species Rubus trivialis, which are self-sterile. 
Consequently, in selecting pollinators we must select such varieties 
as bloom at the same time, regardless of the fact that they are self- 
sterile. 
The blooming period of dewberries lasts about four weeks. Straggling 
blooms may he found at all times during the fruiting season, hut they 
may be safely disregarded, for there are not enough of them to warrant 
the time wasted in the gathering of the resultant fruits. 
The blooming period for the blackberries seems to he a little shorter 
than that for the dewberries. Stragglers are here found mostly among 
the blackberry-dewberry hybrids, while the true blackberries seem to 
have a more definite blooming period. 
Self-fertile vs. Self-sterile Varieties to be Used as Pollinators for the 
Berry Plantation. —From evidence disclosed elsewhere in this bulletin, 
it becomes evident that the requirements of pollinators need not neces¬ 
sarily hinge on the question of self-fertility of varieties, for we found 
that with one exception a self-sterile variety will readily cross with other 
self-sterile varieties; but the fact must be kept in mind that self-sterile 
varieties generally possess in a less degree the qualifications for a good 
pollinator; that self fertile varieties will set fruit in bad as well as in 
good blooming seasons, and that the flowers of self-fertile varieties, whose 
blooming periods do not overlap, will nevertheless produce an abundance 
of perfect fruit, while those of the self-sterile varieties may not. For 
these reasons the self-fertile varieties of dewberries and hybrids that are 
grown either as dewberries or as blackberries ought to be given preference 
whenever possible in the selection of pollinators for the berry plantation. 
Comparisons of Fruits from. Self-fertilized and Cross-fertilized 
Flowers. —Leaving out of consideration the question of parthenocarpy, 
we find that in fruits generally those flowers that are cross-pollinated 
usually produce larger and better fruits than those that are self-polli¬ 
nated. Whether this factor is of sufficient importance in the production 
of dewberries and of blackberries is a question worthy of consideration. 
In order to investigate the probable effect of cross-pollination over 
that of self-pollination with varieties of dewberries and blackberries and 
their hybrids, two lots of flowers from each of two representative varie¬ 
ties of each type were selected. Lucretia and Austin were chosen to 
represent the dewberries; Early Harvest and Snyder, the blackberries; 
and Wilson and Cox, the hybrids. Each lot of the different varieties 
consisted of large branches with flowers clusters in as nearly the same 
stage of maturity as it was possible to find. All of these branches were 
covered alike with cloth bags; the first lot, in order to prevent cross- 
