492 On the Genetics of Tetraploid Plants in P. sinensis. 



relationships between the factors and the chromosomes. Although the fact 

 that the duplication of the chromosomes has been accompanied by a dupli- 

 cation of the series of factors may seem at first sight to suggest a definite 

 connection between chromosomes and factors, yet, on the other hand, the 

 tetraploid number of chromosomes may be nothing more than an index of 

 the quadruple nature of the cell as a whole. The case is, in fact, exactly 

 analogous to the ordinary zygotic cell, which has 2x chromosomes and in 

 which each factor is represented twice. But there are grounds for 

 believing that further experiment with tetraploid plants may have a 

 direct bearing in this connection, for some of the experiments have 

 already given an unmistakable indication of the existence of special 

 inter-relations (in the form of coupling or repulsion) between certain 

 factors in the teti*aploid Primulas. The work has not yet gone far enough 

 to permit of any useful statement of the results, but it is obvious that it will 

 provide a new opportunity for the study of the mutual relations between 

 factors in heterozygous plants, particularly as to whether or not special 

 inter-relations may occur between the two factors of the same kind {i.e. 

 between A and A'), and as to whether either of the factors of one kind may 

 have relations with either factor of another kind {i.e. A with either B or B', 

 and conversely), or whether the A and B factors form one pair of related 

 factors, the A' and B' an independent pair, so that A may have special 

 relations with B but none with B', and conversely. 



Part of the expenses of this work have been defrayed by grants from the 

 Eoyal Society and from the British Association. I wish also to express my 

 great indebtedness to the authorities of the John Innes Horticultural 

 Institution for the facilities for work and the help they have so freely 

 given me. 



