14 N. H. Agricultural Experiment Station [Bulletin 274 



varieties. Heavier sets of fruit have consistently been obtained in such 

 areas as compared with other parts remote from these pollenizer trees. 

 This can be checked through hand-pollination experiments. 



Even though liberally supplied with bees, plantings of large blocks of a 

 single variety of apple such as Delicious, for instance, have often failed to 

 set fruit. This has frequently led to the supposition that under existing 

 environmental conditions the lack of set was due to self-unfruitfulness. 

 This would later be confirmed when good sets of fruit were obtained after 

 the introduction of other varieties to act as pollenizers. Emphasis should be 

 placed on the fact that one must be sure lack of bees is not the cause of 

 poor pollination before concluding that the trouble is lack of good pol- 

 lenizers. 



From general observations and from carefully controlled experiments, 

 it has been possible to classify most of the commercial varieties of apples 

 into a number of classes ranging from the self-fruitful — those setting fruit 

 with own pollen — to the kinds which are entirely self-unfruitful. A good 

 many varieties will set a small amount of fruit through self-pollination, but 

 this will not be enough to produce a paying crop. 



Given varieties in different sections of the country differ as to the degree 

 of self-unfruitfulness. Generally the soil and cHmatic conditions are widely 

 different in places where such wide differences in self-fruitfulness and un- 

 fruitfulness exist. A good example is the Mcintosh which is partially self- 

 unfruitful in the humid eastern half of North America, yet is reported as 

 being self-fruitful in Montana and Washington, the arid northwestern sec- 

 tion of the United States. Baldwin, on the other hand, is considered self- 

 fruitful in northern New England, but has been reported as being self- 

 unfruitful in some other sections. 



Among the varieties that are self-unfruitful to a great enough degree to 

 reduce the set below any desirable commercial quantity in New Hampshire, 

 may be listed Mcintosh, Delicious, Gravenstein, Rhode Island Greening, 

 Northern Spy, Wagener, Fameuse, Golden Delicious. Winesap, Stayman 

 Winesap and Winter Banana. Certainly many other varieties also fall into 

 this class, but it is not within the scope of this bulletin to include them. 

 Some are new and have not as yet been thoroughly tested at this or nearby 

 stations. Others are now obsolete or of little or no commercial importance. 



Cross-unfniitfulness. Cross and inter-unfruitfulness may also occur 

 among certain varieties. This fact is of importance to the apple grower 

 because plantings are often made of varieties which may pollinate in one 

 direction but not in the other. Gravenstein will not satisfactorily pollinate 

 Mcintosh, for example, but Mcintosh is an excellent pollenizer for Grav- 

 enstein. Again. Northern Spy and Rhode Island Greening in some sections 

 seem among themselves to be unfruitWl, neither being able to set a crop of 

 fruit when one pollenizes the other. ^^S'^r^^ J 'y"^'->''-i< '>-■--(■''] ^ 



Inter-fntitfuhicss. Fortunately a few varieties are mter-f ruitful ; that 

 is, cross-jiollination is successful in both directions. This minimizes the 

 nvunber of varieties to be planted in a given orchard and may be an advan- 

 tage under many conditions. Cortland and Mcintosh are good examples. 

 They will satisfactorily pollenize one another. Gravenstein and Delicious, 

 Gravenstein and Wagener, and Mcintosh and Oldenburg are similar inter- 

 fruitful combinations. 



