2736 



POLLEN 



POLLEN 



with other fruits, self-sterility is purely relative; under 

 favorable conditions these varieties are able to set 

 fruit without cross-pollination." Powell proved that 

 in different parts of the Delaware-Maryland peninsula 

 the Kieffer pear is self-sterile, partially self-fertile, 

 or completely self-fertile. The Ben Davis apple is 

 self-sterile in Vermont, according to Waugh, but self- 

 fertile in Kansas, in the experiments of Greene. 

 Bartlett pear is self-sterile in most of the Atlantic 

 States, but usually self-fertile on the Pacific Coast. 

 Beach found that varieties of grapes which are weakly 

 self-fertile vary in this respect in different localities, 

 and even in different parts of the same vineyard, 

 being entirely self-fertile in one place and completely 

 self-sterile in another. It is quite evident that the 

 degree of adaptation of a variety to its environment 

 of soil and climate has much to do with its ability to 

 fruit abundantly with its own pollen. 



It is not possible, therefore, to give a list of varieties 

 that are self-sterile, and another list of those that are 

 self-fertile, that would have more than local applica- 

 tion. There are certain sorts, however, that are less 

 dependable in this respect than others. Out of eighty- 

 seven varieties of apples tested in Oregon by Lewis, 

 fifty-nine were self-sterile, fifteen self-fertile, and thir- 

 teen partially self-fertile. Powell found practically all 

 the commerical varieties of apples in Delaware self- 

 sterile, except several summer sorts. Some of the 

 prominent commercial varieties that are usually more 

 or less uncertain are: Arkansas (Mammoth Black Twig), 

 Gravenstein, Grimes, Jonathan, King (of Tompkins), 

 Limbertwig, Paragon, Northern Spy, Ortley, Rome, 

 Spitzenburg (Esopus), Twenty Ounce. Winesap. 

 Among those generally quite dependable are Ben 

 Davis, Baldwin, Oldenburg, Rhode Island Greening, 

 Yellow Transparent, Yellow Newtown. 



Anjou, Bartlett, Clairgeau, Clapp, Howell, Kieffer, 

 Lawrence, Nelis, and Sheldon pears are frequently 

 uncertain, while Angouleme (Duchess), Bosc, Flemish, 

 and Seckel are usually self-fertile. Practically all the 

 varieties of Japanese and native plums are self-sterile, 

 the single exception, according to Waugh, being Robin- 

 son. Wild Goose and Miner are notoriously infertile. 

 Hooper and Backhouse report that the European varie- 

 ties are largely self-sterile in England, but in America 

 the defection is confined chiefly to Coe, French Prune, 

 and Italian Prune. The experiments of Close, Whitten, 

 and Howard, indicate that all the leading varieties of 

 peaches are self-fertile, and are not benefited by cross- 

 pollination. In Germany, however, Ewart finds 

 peaches "sparingly self-sterile." No cherries are known 

 to be self-sterile, although Napoleon, Belle de Choisy, 

 and Reine Hortense have that reputation among com- 

 mercial growers. 



Of one hundred and forty-five varieties of grapes 

 tested by Beach, thirty-one were self-fertile, forty-one 

 self-sterile, and seventy-three uncertain. Brighton, 

 Herbert, Lindley, Merrimac, Salem, Wilder, and other 

 hybrid varieties are decidedly unfruitful with their own 

 pollen; while Concord, Delaware, Diamond, Niagara, 

 Winchell, and Worden are among those strongly self- 

 fertile. Reimer found the Scuppernong and other varie- 

 ties of the Muscadine grape so defective in pollen that 

 they are fruitful only when planted near male vines of 

 the Muscadine. No varieties of the quince, raspberry, 

 currant, gooseberry, or strawberry have been found 

 self-sterile, but many varieties of strawberries lack 

 well-developed stamens and so must be planted near 

 perfect-flowered sorts. 



A self-sterile variety often may be made fruitful by 

 planting near it another variety to supply pollen; or 

 by top-grafting part of the tree with cions of another 

 sort. No benefit is derived from other trees of the same 

 variety, even if brought from a distance, since all are 

 but divisions of the same original seedling. In the 

 selection of a pollinizer, several points must be con- 



sidered: (1) The two sorts must blossom approximately 

 at the same tune in order that cross-pollination may be 

 possible. The transfer of pollen from one variety to 

 another is performed mainly by insects. Waugh and 

 Backhouse have shown that practically none of the 

 pollen of the plum and other stone-fruits is carried by 

 wind, it being moist and sticky. The same is true of 

 pears, but apple pollen is somewhat drier and is wind- 

 blown to a slight extent. The honey-bee is the most 

 important pollen-carrier. Hooper estimates that in 

 England 80 per cent of the cross-pollination is done by 

 the hive bee, 15 per cent by various wild bees, especially 

 the bumblebee, and 5 per cent by miscellaneous insects. 

 In tree-fruits it is necessary to select varieties that come 

 into bearing at about the same age, otherwise one might 

 be without cross-pollination for the first two or three 

 years. Several state experiment stations haye published 

 lists of varieties blossoming at the same tune, for the 

 guidance of the planter. See New York (Geneva) 

 Bulletin No. 407. (2) There should be an affinity 

 between the two varieties, so that the self-sterile sort 

 may find the pollen of the other acceptable. This can 

 be determined only by hand-crossing. Beach found 

 that the pollen of self-sterile varieties of grapes is 

 practicably incapable of fertilizing other varieties; but 

 this does not hold for tree-fruits since two self -sterile 

 varieties planted together usually are mutually fruit- 

 ful. Powell found no affinity between Paragon and 

 Stayman apples; Kerr none between Wild Goose and 

 Whitaker plums, and there are a number of other 

 instances. Undoubtedly some varieties are more accep- 

 table as pollinizers of a self -sterile variety than others. 

 Spitzenburg apples produced by Lewis from Jonathan 

 pollen averaged 144 grams in weight; from Baldwin 

 pollen, 157 grams. In general, however, varieties of the 

 same species that blossom simultaneously cross-fertilize 

 readily, and there is no appreciable and constant differ- 

 ence in the fruit. (3) In commercial orchards the 

 pollinizer should be a standard variety, valuable for 

 market. (4) It should produce a large amount of 

 pollen. Winesap produces little pollen; it would be 

 unsatisfactory as a pollinizer for other sorts; Grimes, 

 Ben Davis, and Rome are abundant pollen-bearers. 



Cross-pollinated fruits may be larger and heavier 

 than self-pollinated fruits, but there is rarely any other 

 influence. The shape, color, flavor, and keeping qual- 

 ity remain the same, regardless of the variety selected 

 as a pollinizer. Kieffer pears pollinated with Seckel look 

 and taste no different from Kieffer pears pollinated with 

 Le Conte. Many supposed instances of the immediate 

 influence of pollen have been recorded, but in most 

 cases proof is lacking that the changes were not due to 

 bud- variation. It cannot be doubted that this influence 

 is exerted occasionally, but certainly much less fre- 

 quently than is commonly supposed. 



In small orchards there is no need of mixing the 

 varieties with special reference to cross-pollination. In 

 orchards covering more than 10 acres, it is desirable to 

 intersperse the varieties at regular intervals. It is more 

 convenient in spraying, harvesting, and other orchard 

 operations to plant the pollinizer in a solid row instead 

 of mixing it in the rows with the self -sterile sort. If the 

 pollinizer is not very valuable, one row in ten may be 

 sufficient; but usually one in four to six is safer. If the 

 pollinizer is a valuable variety, the two should be 

 alternated in blocks of four to six rows each. It is not 

 necessary to plant more than one yariety as a pollinizer. 



Orchard pollination, however, is a broader problem 

 than the mere detection of varieties that are inclined 

 to be unfruitful when planted alone, and discovering 

 which are the best pollinizers for each of them. Experi- 

 ments in crossing and observations in orchards indicate 

 that nearly all varieties, whether self-sterile or self- 

 fertile, will produce more or better fruit with foreign 

 pollen than with their own. Powell found that some 

 self-fertile trees of Kieffer in Delaware bore a light crop 



