SPECIES HYBRIDIZATION 243 
the admixture be relatively slight, the inharmonious elements may not 
greatly affect the workings of the reaction system, and there would result 
individuals showing practically the entire set of characters of one or the 
other parent, and such individuals would be fully fertile. A slightly 
greater proportion of inharmonious elements in the reaction system would 
result in such profound disturbances in its functioning as to produce the 
abnormal individuals of various kinds which make up so large a propor- 
tion of the progeny from such parentage. When the proportions of 
inharmonious elements in the gametes becomes still greater, they fail to 
function at all. It is upon the formation of such non-functional gametes 
or the attempt to produce them, that the partial sterility of the hybrid 
depends, and since in this particular case these form by far the greater 
proportion of gametes, the hybrid is very nearly completely sterile. 
The relations may be illustrated by Table XX XVIII which represents 
Taste XX XVIII.—REcOMBINATION SERIES IN GAMETES OF F, oF N. tabacum X N. 
sylvestris 
fe Tabacum: | Proportionat P h P rh 
Condition of aylvestria | numberof | pollinated with pollinated with 
gametes chromosomes | gametes N. tabacum N. sylvestris 
| 
24:0 | 1 | Plants Pecmbline | Plante resembling 
23:1 24 the N. tabacum) the F, and ab- 
Functional...... 22:2 276 parent and of vari- | normal plants but 
21:3 2,024 ous degrees of | all nearly com- 
20:4 10,626 fertility pletely sterile 
19:5 42,504 
18:6 134,596 
17:7 346,504 
16:8 236,321 
15:9 1,307,504 
14:10 1,961,256 
13:11 2,496,144 
Non-functional . 12:12 2,705,456 | No viable seeds No viable seeds 
11:13 2,496,144 
10:14 | 1,961,256 
9:15 1,307,504 
8:16 736,321 
7:17 346,504 
6:18 134,596 
5:19 42,504 | Plants resembling | Abnormal, infertile 
4:20 10,626 the F, hybrid and | plants and fertile 
3:21 2,024 nearly completely | plants closely re- 
Functional...... 2:22 276 sterile sembling N. syl- 
1:23 24 |, vestris 
0:24 1 ‘ 
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