562 Report op the Horticulturist 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 he 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 self- 

 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, 



