16 



JOUENAL OF THE EOYAL HORTICULTUEAL SOCIETY. 



same time that the relation of each two different characters in hybrid 

 connection is independent of the other diff^erences in tlie two original 

 2X1 rental stocks. 



If n represent the number of the characteristic differences in the 

 two original stocks, 3" gives the number of components of the combina- 

 tion series, 4" the number of individuals which belong to the series, 

 and 2" the number of connections which remain constant. The series 

 therefore embraces, if the original stocks differ in four characters, 3''=81 

 ■component classes, 4^ = 256 individuals, and 2* = 16 constant forms; 

 or, which is the same, among each 256 offspring of the hybrids there are 

 •81 different combinations, 16 of which are constant. 



All constant combinations which in Peas are possible by the com- 

 bination of the said seven characteristic features were actually obtained 

 by repeated crossing. Their number is given by 2"= 128. Thereby is 

 simultaneously given the practical proof that the constant characters 

 ichich appear in various forms of a plant group may he obtained in all 

 the associations which are possible according to the laws of combination 

 by means of repeated artificial fertilisation. 



As regards the flowering time of the hybrids, the trials are not yet 

 concluded. It can, however, already be stated that the period stands 

 almost exactly between those of the seed and pollen parents, and that the 

 development of the hybrids with respect to this character probably happens 

 in the same way as in the case of the other characters. The forms which 

 are selected for trials of this class must have a difference of at least 

 twenty days from the middle flowering period of one to that of the other ; 

 furthermore, the seeds when sown must all be placed at the same depth 

 in the earth, so that they may germinate simultaneously. Also, during 

 the whole flowering period, the more important variations in temperature 

 must be taken into account, and the partial hastening or delaying of the 

 flowering which may result therefrom. It is clear that this experiment 

 presents many difficulties to be overcome and necessitates great 

 ^jttention. 



If we endeavour to collate in a brief form the results arrived at, 

 vs'e find that those difterentiating characters which admit of easy and certain 

 recognition in the trial plants all behave exactly alike in their hybrid 

 associations. The offspring of the hybrids of each pair of differentiating 

 characters are, one-half, hybrid again, while the other half are constant 

 in equal proportions with the characters of the seed and pollen parents 

 respectively. If several differentiating characters are combined by cross- 

 fertilisation in a hybrid, the resulting offspring form the components of a 

 combination series in which the developmental series for each pair of 

 differentiating characters are united. 



The uniformity of behaviour shown by the whole of the characters 

 submitted to trial permits, and fully justifies, the acceptance of the 

 principle that a similar relation exists in the other characters which 

 appear less sharply defined in plants, and therefore could not be included 

 in the separate experiments. An experiment with peduncles of different 

 lengths gave on the whole a fairly satisfactory result, although the differ- 

 entiation and serial arrangement of the forms could not be effected with 

 that certainty which is indispensable for correct experiment. 



