. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. HYBRIDS, SEGREGATION 385 the latter bears only one allelomorph. It is only on this basis that the reappearance of a latent character in the second genera- tion can be explained. If the dominant and recessive characters of an aUelomorphic pair are represented by A and a respectively, then the fertilised eggs produced by crossing will all have the constitution Aa, and the resulting plants will all show the dominant character only ; such individuals are spoken of as heterozygotes. It is believed that in these hy
. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. HYBRIDS, SEGREGATION 385 the latter bears only one allelomorph. It is only on this basis that the reappearance of a latent character in the second genera- tion can be explained. If the dominant and recessive characters of an aUelomorphic pair are represented by A and a respectively, then the fertilised eggs produced by crossing will all have the constitution Aa, and the resulting plants will all show the dominant character only ; such individuals are spoken of as heterozygotes. It is believed that in these hybrids, during the" formation of each tetrad of spores, and in conjunction with the reduction division (see p. 306), the characters A, a become separated, so that each spore, and consequently each of the. Fig. 224.—Geum rivals (A), Geuni urbanum (C), and the hybrid between them, Geum intermedium (B), In each case the receptacle and calyx arc shown, together with an enlargement of a single carpel. gametes, to which it ultimately gives rise, bear either A or a. It is probable, moreover, that the determinants for these charac- ters are contained within the nuclei of the sexual cells (p. 390). During self-fertilisation, and assuming the gametes to meet according to the laws of chance, there are four possible com- binations : viz. (i) a male gamete bearing A and a female bearing A; (2) a male bearing A and a female bearing a; (3) a male bearing a and a female bearing A ; and (4) a male bearing a and a female bearing a. That is to say, among each four fertilised eggs that result, there will probably be i AA, 2 Aa, and i aa. Seeing that A is invariably dominant, there will in the second generation be three individuals with the dominant to one indi-' 25. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Fritsch,
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