562 Report oF tHE HorticuLtTurist OF THE 
3. Pollen of self-sterile grapes may successfully fertilize other 
grapes. 
4, Pistils of self-sterile grapes are usually well developed. They 
develop into fruit when cross-pollinated. 
In view of the following considerations the most satisfactory ex- 
planation of self-sterility which can be presented appears to be that 
with self-sterile grapes there is a lack of affinity between the pollen 
and the pistils of the same variety. 
1. Nearly all of the self-sterile list and of the list of varieties 
which give very imperfect self-fertilized clusters are known to be 
hybrids. Possibly all are hybrids. 
2. Self-sterility is often found among plant hybrids. 
The variability in the degree of self-fertility which has been 
observed with some varieties seems to be due to the production of 
more vigorous pollen or the development of a greater affinity 
between the pollen and pistils of the same variety under espe- 
cially favorable circumstances. Thus Brighton is generally sclf- 
sterile. Under especially favorable conditions it has overcome 
self-sterility to so great an extent that a few self-fertilized fruits 
have developed. See Plate LI, Figure 1. 
LENGTH OF STAMENS AS AN INDICATION OF 
SELF-FERTILITY. 
An examination of the list of cultivated varieties included in 
these experiments, omitting Hopkins and Shelby, the stamens of 
which have not been observed, shows that only those varieties 
which have long stamens produce marketable clusters of fruit 
where the blossoms are bagged. This is certainly strong evidence 
that varieties having short stamens are not able of themselves to 
produce marketable clusters of fruit. 
Twenty-six of the cultivated varieties which were tested, while 
not completely self-sterile, were nevertheless unable to produce 
marketable clusters where the blossoms were bagged. Eighteen of 
these have long stamens and eight have short stamens. 
There were forty cultivated varieties which, so far as tested, 
