THE PHENOMENA OF REVERSION 



503 



D. chi-iensis 9 x barbatiis $ by the pollen of B. barbatns. The 

 formula of this hybrid would therefore be — Dianthus{chinensisy. 

 barbatns) 9 x barbatns $ , or in more general terms by (A + B) 

 9 X A J. 



For the sake of simplicity let us assume that the number of 

 idants and force of transmission is similar in the case of both 

 ancestral species. We will suppose that sixteen idants* are 

 arranged in a circle, as represented in Fig. 22, I. In the 

 production of the .^ hybrid, eight idants of A combine with 



Fig. 22. — Diagram of the cojiiposition of the germ-flasm in hybrids. — I. The 

 germ-plasm of the parental species, each composed of sixteen idants; A, Dianthus 

 chinensis; B, Dianthus barbatns. \\. Germ-plasm of the hybrid, composed of 

 eight idants from A and eight from B: s, the plasm of section, which may be 

 rotated. in.,IV., V. Three of the possible combinations of the germ-plasm which 

 might arise by crossing hybrid II. with the parental species B. III. A true three- 

 quarter hybrid. IV. Contains idants of the parental species B only. V. Contains 

 nine idants from B and seven from A. 



eight idants of B ; the mother germ-cells of this hybrid will 

 therefore always contain 8 A x 8B idants (Fig. 22, II.). The 

 reducing division then occurs, and bisects the circle at some 

 point. Fig. 22, II., will make it apparent that by rotating the 



* We might just as well speak of 'ids' as 'idants ' in this illustration. 

 I have referred to the idants simply because they are visible units, and not 

 merely hypothetical structures, and also because the number of idants may 

 be assumed to be less than that of the ids, and is thus more easily con- 

 trollable. 



