350 JOURNAL OF THE ROYAL HORTTCULTlTRATi SOCIETY, 



GONTETBUTIONS FROM THE WISLEY LABORATORY. 

 XII.— Pollination in Orchards. — I. 



By F. J. Chittenden, F.L.S. 



Among the many factors upon which fruitfiilness of orchard trees 

 depends, cross-poUi nation is, as a rule, of first-rate importance. It is 

 now known that a large numher of apples, pears, and plums are self- 

 s.terile,* i.e. they fail to set fruit unless their flowers are pollinated 

 with pollen from another variety of the same kind of tree. 



Self-sterility is , a widespread phenomenon in the vegetable king- 

 dom,! for which we have at present no adequate explanation, but when 

 it occurs in annuals, e.g., Papaver B^hoeas, it appears sufficient if 

 pollen is transferred from the anthers of one plant to the stigma of 

 any other; but with apples, pears, and plums the case is different. 

 The trees of any variety of apple, pear, or plum, though in some sense 

 individuals, yet, since they are all derived by vegetative propagation 

 from one original stock, are, from another point of view, all parts 

 of one individual: tliey retain the same innate characters as those 

 possessed by the original from which they were divided, and their 

 protoplasm is directly derived from the protoplasm of their common 

 parent ; it is not the result of the combination of two masses of proto- 

 plasm, as it usually is in the case of a plant growing from a seed. The 

 transference of the pollen from a flower on one tree to a flower on 

 another tree of the same variety is, therefore, practically equivalent to 

 transferring it to another flower on the same tree, and it is followed by 

 no more result in the one case than in the other. Cross-pollination 

 must, as a rule, be possible between trees of different varieties if fruit 

 is to be produced. 



This necessity seems to have been first definitely discovered in 

 America :|: for pears, and later the facts were found to apply also io 

 apples. § It has been known in a more or less vague way in this 

 country for some time, though not as widely as it should be. Thougli 

 t he genera] fact is clearly established, detailed knowledge of the behaviour 



* The term " self -sterile " is used in this paper in a rather loose sense 

 for want of a better one. It implies as used here, inability to form fruits with- 

 out the aid of pollen from another variety. In a more accurate sense it 

 would imply inability to form fertile seed without the aid of foreign pollen. 

 Home varieties of pears and apples will produce fruits containing no seeds, and 

 these are therefore self-fertile in the first sense and not in the second ; such 

 varieties have been called by Ewert in Die Partlienocnvpie oder Jiniqfcrnjrucli- 

 iigl-eit cler Ohsthciime (1907) imrthenocni-^vr," a term applied to similar cases 

 })y SoLACOLU in 1905 {Compies Fendus). 



t See, for instance, Focke, " Ueber Unf ruchtbarkeit , bei Bestaubung mit 

 eigenem Pollen " in Ahhondlungen heraiisgegehm rom iiaturinssensrhaftliche.i), 

 Vereine zn Bre.men, xii., pp. 409-416, where a list of fifty-seven self-sterile 

 plants is given, a number that might now ea.sily he added to. Pj/rii.s .•<riIir{foJia 

 and Mespilus mgra are there included. 



X See Waite," PolUnation of Pear Floxrem (U.S.A. Dept. Agr., Div. Veg. 

 Path., Bull. 5, 1895). 



§ Watte {U.S.A. Dept. Agr., Year Bool-, 1898, })p. 167-180). 



