Page:Popular Science Monthly Volume 77.djvu/352

346 bear the recessive character. One half of the egg cells, likewise, contain the dominant, and one half the recessive character.

Now, if we could pick out at random any one hundred pollen or male cells to fertilize any one hundred egg or female cells, we can see that there are equal chances for four results. A dominant male cell might meet a dominant female cell, a dominant male cell a recessive female cell, a recessive male cell a dominant female cell, and a recessive male cell a recessive female cell.

We have (D + D), (D + R), (R + D), and (R + R) plants formed in equal quantities, but as the two middle terms are the same, we can reduce the formula to one (D + D) to two (D + R) to one (R + R). But wherever there is a D present in the germ cell, the

 (Helianthemum marifolium). After Kerner and Oliver. 1, single flower; 2, essential organs of flower: course of pollen tubes shown diagrammatically; 3, pollen tubes penetrating the tissue of the pistil; 4, dried pollen grain; 5, pollen grain germinating; 6, ovule.

dominant character shows, while the recessive character is hidden. The one part or 25 per cent, of the individuals showing the character (D + D) will appear just like the two parts or 50 per cent, of the individuals having the character (D + R). Therefore, there will be 75 per cent, of the individuals which will show the dominant or D character, while 25 per cent, will show the recessive or R character. These 25 per cent, showing the R character will ever after breed true, because they contain nothing but the recessive character; while of the 75 per cent, showing the dominant character, one third or those having the pure (D + D) character will breed true in succeeding generations, while the other two thirds having the (D + R) or hybrid character will again split in the next generation.

For all practical purposes in plant breeding the mere fact of segregation is of greatest importance and the complexity of recent Mendelian