Page:Popular Science Monthly Volume 81.djvu/378

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THE POPULAR SCIENCE MONTHLY

which give the results of a portion of the actual experiments. As the experiments were rather extensive, it is not possible here to present anything like the complete material. Only representative matings are here given. Table II. gives the results of some of the B. P. R. × B. P. B. matings in detail, in order to show, not only the accordance between observation and theory, but also the distinctness of the classes of fecundity segregated (shown by the average winter production in each segregated class).

From the data set forth in the above table there can be no doubt as to the fact of the Mendelian segregation of fecundity, nor as to the entire distinctness of the things segregated.

In order to give a general survey of the results, and to demonstrate the reality of segregation over the wide range of material included in the experiments, the summary Table III is presented.

Table III

Showing the Observed and Expected Distribution in Respect of Fecundity of the Adult Female Offspring from all Matings in each of the Classes Tested in the Experiments

 Matings Winter Production of Daughters Class Over 30 Under 30 Zero All Barred Plymouth Rock × Barred Observed 365 .5 259 .5 31 ⁠Plymouth Rock. Expected 381 .45 257 .25 17 .30 All Cornish Indian Game × Indian Observed 2 23 15 ⁠Game. Expected 0 25 15 All F1 (B.P.R. × C.I.G. and reciprocal Observed 36 79 8 ⁠cross). Expected 26 .5 86 .75 9 .75 All F2 (F1 × F1, and F1 × parent Observed 57 .5 98 .5 23 ⁠forms in all possible combinations). Expected 68 .60 95 .00 15 .40

Considering the nature of the material and the character dealt with the agreement shown between observation and hypothesis is certainly as close as could reasonably be expected. Such discrepancies as are shown in the above table are fully discussed and their probable physiological explanations set forth in detail in the complete account of these experiments.

The detailed data given in the complete paper, of which the above discussion and tables give merely a very incomplete abstract, appear definitely to establish the following points:

1. That fecundity in the domestic fowl is inherited strictly in accordance with Mendelian principles.

2. That observed individual variations in fecundity here depend upon two separately inherited physiological factors, ${\displaystyle L_{1}}$ and ${\displaystyle L_{2}}$.

3. That high fecundity is manifested only when both of these factors are present together in the same individual.

4. That either of these factors when present alone whether in homo-