Sex-Reversal and Hereditary Constitution

Sex in Plants.

In the case of plants two sexual forms are recognised, the dioecious (bisexual) and the hermaphroditic. In the former the whole plant generally bears flowers of one kind only, either staminate or pistillate, and these are often referred to as male and female respectively (e.g., hemp, hops). In the hermaphrodite plants staminate and pistillate parts may be borne in the same flower to give the "perfect" flower (e.g., the rose) or they may be borne in different clusters on the same plant (the condition of monoecism) e.g., maize, begonia. It has been argued that monoecism represents a somatic segregation of maleness and femaleness (Bond 5922) but most authorities agree with Emer son (1924) that both the perfect-flowered and the monoecious plants are alike in that the individual plant is hermaphroditic, the difference being merely one of time at which differentiation occurs.

Early genetical study of the dioecious forms showed that in certain of these the "male" is the heterozygous sex (Correns Bryonia dioica 1907; Shull–Lychnis dioica 1910-11). In cytological evidence was presented showing that in several species of dioecious plants the male is digametic, i.e., that the sex determining mechanism is of the X-2X type. (Winge and also Blackburn—Lychnis, Kihara and Ono—Rumex acetosa; Santos Elodea canadensis; Winge--V allisneria spiralis, Humulus Lupulus, Humulus japonica.) In no case thus far has the female proved to be digametic.

There is one type of sex-determining mechanism in plants which is not known in animals. In the liverworts and kindred forms the gametophyte generation is the important and con spicuous one. Allen (1917) found in Sphaerocarpus that the male gametophyte has a Y-chromosome, the female gametophyte an X, whereas the sporophyte has the 2N number of chromo somes including the very unequal XY pair.

Two sex-linked characters have been identified (Shull, 1914), a narrow rosette leaf in Lychnis and (Winge, 1928) and a chlor ophyll deficiency in the same plant. Winge considers that the

gene for this character is Y-borne.

Sex-reversal has been reported frequently in dioecious plants (Schaffner, 1918-23). The transformation is conditioned by age, nutrition, length of day, etc.

Correns (1918-22) has investigated aberrant sex-ratios in Lychnis dioica and explained the excess of females on the basis of a more rapid growth of the pollen-tubes from grains bearing the X-chromosome.

Emerson (1924) has adduced evidence showing that in maize, as in Drosophila, it is the genic balance which is the effective factor in sex-determination. He suggests that in most dioecious plants this balance is decisive in the usual environments so that the individual is either a male or else a female whilst in the hermaphrodite it is so delicate that the characters of both sexes are expressed.

Chemical Tests and Sex-identification.

A chemical test for the identification of sex was introduced by Manoiloff (1922 23). The method is based upon the assumption that there are specifically different chemical substances in the blood of male and female. Subsequent work by others has seemed to show that different concentrations of serum proteins in the blood can ex plain the Manoiloff reaction. Schratz (1926) concludes that the reaction does not show a greater accumulation of oxides in female blood and that the reaction of Bernatzki (1924) is of greater value. Galwialo and others (1926) are of opinion that the test is not specific but is dependent entirely upon the protein content of the substance investigated. Luttge and v. Mertz (1926) describe a technique for the serological identification of sex, which, judging on the basis of early investigations, apparently gives satisfactory results.