HYBKIDIZATIOtf. 643 



Reversion. The impregnation of the ovules of hybrids by the pollen of 

 plants of either parent species produces more fertile seeds than are formed 

 after self-fertilization of hybrids. The progeny in such cases return more 

 or less to the parent type, on the side from which the pure pollen 

 comes, and by a repetition of such fertilization the hybrid characters are 

 lost in a few generations. 



It is an interesting fact that the ovules of hybrids are sometimes more 

 freely fertilized by pollen of a strange but pure species, than by their 

 own : thus the hybrid Nicotiana paniculato-rustica, which usually did not 

 ripen more than 13 good seeds in a capsule, produced with the pollen 

 of N. paniculata 36, with N. rustica 20, and with the pollen of N. Langs- 

 dorfii (a totally new element in the crossing) 16. In another experiment, 

 when this hybrid produced no seed by self-fertilization, 10 good seeds 

 resulted from crossing with N. Langsdorjii. (For a general review of the 

 subject of Hybridization, see Darwin, ' Variations of Animals and Plants/ 

 ed. 2, vol. ii. p. 157, and Anderson Henry, Proc. Soc. Bot. Edinburgh, 

 1867.) 



A curious phenomenon has been observed in the garden plant called 

 Cytisus Adami, obtained either by grafting or by true hybridation of the 

 two kinds of Laburnum, Cytisus Laburnum and C. purpureus. The 

 plants in many instances exhibit a partial separation or dissolution of 

 the hybrid characters in the products of different leaf-buds : on the same 

 tree in which part of the branches bear blossom of the hybrid character, 

 other shoots occur, some of which revert to the character of Cytisus 

 Laburnum, others to that of C. purpureus, the other parent. In some 

 of the shoots, moreover, unequally combined characters of the parents are 

 observed in different flowers of the same raceme. 



In some cases it has been found that the reverted or pure shoots bear 

 perfect seeds, while the hybrid blossoms were barren. 



Cytisus Adami has generally been supposed to be an ordinary hybrid ; 

 but it has recently been stated that it originates when C. purpureus is 

 grafted on Cytisus Laburnum, offering thus an instance of affection of 

 the stock by the scion analogous to that of the variegated Jasmine and 

 Abutilon referred to previously (p. 618). If this prove true, it will be 

 a most important physiological fact, opening up a very interesting field 

 for experiment, and likely to lead to practical results of high value in the 

 cultivation of fruit-trees. Certain sports of Roses have also been accounted 

 for on the supposition that they have originated as graft-hybrids ; but 

 the evidence on the point is not as yet sufficiently conclusive. 



In some cases the action of hybrid pollen is made manifest in the 

 production of changes in the envelopes of the seed, and even in the 

 appearance of the fruit, so that the influence has been exerted not 

 only on the offspring but also on the mother plant. As an illustration 

 may be cited the case recorded by Vilmorin of a yellow-seeded Maize 

 producing black seeds when crossed with pollen from a black variety. 

 Such cases, however, require strict scrutiny. (See Laxton, Proceedings 

 Internat. Bot. Congress, London, 1866, p. 156, and Clarke in the same 

 volume, p. 143 ; Darwin, ' Animals and Plants under Domestication/ ed. 2, 

 p. 427 ; Maximowicz, as translated by Dyer in Journ. Hort. Soc. London, 

 vol. iii. p. 161, 1872.) 



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