150 HORTICULTURE, FORESTRY, FLORICULTURE 



Cross-pollination of varieties is no longer a theory ; it is an established 

 orchard practice. 



Varieties Which Are Often Self-Sterile. Self-sterility is not a 

 constant character with any variety. It is influenced by the condi- 

 tions under which the tree is grown, as are the size, shape and color 

 of the fruit. The adaptation of a variety to soil and climate has 

 much to do with its self-fertility, and if a tree is poorly nourished 

 it is more likely to be infertile with its own pollen. No one can sepa- 

 rate varieties of fruit into two definite classes, the self-sterile and the 

 self-fertile. Thus Bartlett and Kieffer are often self-sterile, but there 

 are orchards of both which are self-fertile. The same may be said of 

 many other varieties. The best that can be done, therefore, is to give 

 a list of those varieties w r hich tend to be more or less self-sterile and 

 which it would be unsafe to plant alone. 



Following is a conservative list of these risky varieties, drawn 

 both from experimental work and from the reports of over five hun- 

 dred fruit growers: Pears Angouleme (Duchess), Bartlett, Clapp, 

 Idaho, Kieffer, Nelis. Apples Bellflower, Primate, Spitzenburg, 

 Willow Twig, Winesap. Plums Coe Golden Drop, French Prune, 

 Italian Prune, Kelsey, Marianna, Miner, Ogon, Peach Satsuma, Wild 

 Goose, and according to Waugh and Kerr, all other varieties of native 

 plums except Robinson. Peach Susquehanna. Apricot White 

 Nicholas. Cherries Napoleon, Bell de Choisy, Heine Hortense. 

 Most of these varieties are self-fertile in some places, but the weight 

 of evidence shows them to be uncertain. 



I It must not be inferred that all other varieties are always able 

 to set fruit when planted alone. There are some, however, which have 

 exceptionally good records for fruitfulness when planted in solid 

 blocks, other conditions being favorable. Among these are: Apples 

 Baldwin, Ben Davis, Fallawater, Janet, Oldenburg, Rhode Island 

 Greening, Red Astrachan, Smith Cider. Plums Burbank, Brad- 

 shaw, DeSoto, Green Gage, Lombard, Robinson and some of the 

 common blue Damsons. 



The problem of self-sterility is as much a study of conditions as 

 of varieties. We can set no limits ; we can only indicate tendencies. 



Selecting the Pollinizer. There are two points to be considered 

 when selecting a pollinizer for any self-sterile variety; these are 

 simultaneous blooming and mutual affinity. 



The first and most important point is that the two shall blossom 

 together, since the only way in which a pollinizer can make a self- 

 sterile variety fruitful is by supplying it with pollen. This means 

 that the pistils of the self-sterile variety must be receptive when the 

 stamens of the pollinizer are ripe, which is possible only with simul- 

 taneous blooming. 



The comparative blooming of varieties is more or less a local 

 problem. Differences of latitude, altitude, soil, nearness to large 

 bodies of water, and weather conditions during the blooming season 

 not only hasten or retard the time of blooming, but also disturb 

 the order in which the different varieties open. Varieties blossom- 

 ing together at one place may not at another. The best that can be 



