EXPEEIMENTS IN PLANT HYBRIDISATION. 



31 



formation varies in many species, so that frequently a species A can be 

 transformed into a species B a generation sooner than can species B into 

 species A. He deduces thereform that Koh^euter's opinion can hardly be 

 maintained that " the two natures in hybrids are perfectly in equilibrium." 

 It appears, however, that Kolreuter does not merit this criticism, but that 

 Gartner rather has overlooked a material point, to which he himself 

 elsewhere draws attention, viz. that " it depends which individual is chosen 

 for further transformation." Experiments which in this connection were 

 carried out with two species of Pisum demonstrated that as regards the 

 choice of the fittest individuals for the purpose of further fertilisation it 

 may make a great difference which of two species is transformed into the 

 other. The two trial plants differed in five characters, while at the same 

 time those of species A were all dominant and those of species B all recessive. 

 For mutual transformation A was fertilised with pollen of B, and B with 

 pollen of A, and this was repeated with both hybrids the following year. 



With the first trial - there were eighty-seven plants available in the 



A. 



third trial year for the selections of individuals for further crossing, and 



these were of the possible thirty- two forms ; with the second trial ^ 



B 



seventy-three plants resulted, which agreed throughout perfectly in habit 

 with the 2yollen parent ; in their internal composition, however, they must 

 have been just as varied as the forms of the other trial. A definite 

 selection was consequently only possible with the first trial ; with the 

 second some plants selected at random had to be excluded. Of the latter 

 only a portion of the flowers were crossed wdth the A pollen, the others 

 were left to fertilise themselves. Among each five plants which were 

 selected in both trials for fertilisation there agreed, as the following 

 year's culture showed, with the pollen parent : — • 



Second Trial. 



— in all characters 



— 4 

 2 plants „ 3 „ 

 2 „ 2 ,, 

 1 plant „ 1 character 



In the first trial, therefore, the transformation was completed ; in the 

 second, which was not continued further, two more fertilisations would 

 probably have been required. 



Although the case may not frequently occur that the dominant 

 characters belong exclusively to one or the other of the original parent 

 plants, it will always make a difference which of the two possesses the 

 majority. If the pollen parent shows the majority, then the selection of 

 forms for further crossing will afford a less degree of security than in the 

 reverse case, which must imply a delay in the period of transformation, pro- 

 vided that the trial is only considered as completed when a form is arrived 

 at which not only exactly resembles the pollen plant in form, but also 

 remains as constant in its progeny. 



Gartner, by the results of these transformation experiments, was led 

 to oppose the opinion of those naturalists who dispute the stabihty of 



First Trial. 

 2 Plants 



