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JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



species A would change into the species B. Gartner alone has effected thirty 

 such trials with plants of genera Aquilegia, DiantJms, Geiivi, Lavatera, 

 Lychnis, Malva, Nicotiana, and CEnothera. The period of transformation 

 w^as not alike for all species. While with some a triple fertilisation 

 .sufficed, with others this had to be repeated five or six times, and even in the 

 same species fluctuations were observed in various experiments. Gartner 

 iiscribes this difference to the circumstance that " the typical force by 

 which a species, during reproduction, effects the change and transformation 

 of the maternal type varies considerably in different plants, and that, 

 consequently, the periods must also vary within which the one species is 

 changed into the other, as also the number of generations, so that the 

 transformation in some species is perfected in more, and in others in 

 fewer generations." Further, the same observer remarks " that in these 

 transformation trials a good deal depends upon which type and which 

 individual be chosen for further transformation." 



If it may be assumed that in these trials the development of the forms 

 resulted in a similar way to that of Pisum, the entire process of trans- 

 formation would find a fairly simple explanation. The hybrid forms as 

 many kinds of egg cells as there are constant combinations possible of the 

 characters conjoined therein, and one of these is always of the same kind 

 as the fertilising pollen cells. Consequently there always exists the 

 possibility with all such trials that even from the second fertilisation there 

 may result a constant form identical with that of the pollen parent. 

 Whether this really be obtained depends in each separate case upon the 

 number of the trial plants, as well as upon the number of differentiating 

 characters which are united by the fertilisation. Let us, for instance, assume 

 that the plants selected for trial differed in three characters, and the 

 species ABC is to be transformed into the other species abc by repeated 

 fertilisation with the pollen of the latter ; the hybrids resulting from the 

 first cross form eight different kinds of egg cells, viz. : 



ABC, ABc, AbC, aBC, Abc, aBc, abC, abc. 



These in the second trial year are united again with the pollen cells 

 abc, and we obtain the series 



AaBbCc + AaBbc + AabCc + aBbCc -f Aabc + aBbc + abCc + abc. 



Since the form abc occurs once in the series of eight components, it is 

 consequently little likely that it would be missing among the trial plants, 

 even were these raised in a smaller number, and the transformation would 

 be perfected already by a second fertilisation. If by chance it did not appear, 

 then the fertilisation must be repeated with one of those forms nearest akin, 

 Aabc, aBbc, abCc. It is perceived that such an experiment must extend 

 the farther the smaller the number of trial plants and the larger the 

 number of differentiating characters in the two original species ; and that, 

 furthermore, in the same species there can easily occur a delay of one or 

 even of two generations such as Gartner observed. The transformation of 

 widely divergent species could generally only be completed in five or six 

 trial years, since the number of different egg cells which are formed in 

 the hybrid increases in square ratio with the number of differentiating 

 characters. 



Gartner found by repeated trials that the respective period of trans- 



