Sexualityin Plants

Sexuality in Plants was suspected by Aristotle and Theophrastus, and was more fully recognized by Pliny, these writers being more or less familiar with the division of sexes in the date-palm; but until the 17th century mere difference in habit was often taken to indicate sex, as in the familiar case of the so-called male and lady ferns. Clusius (l526-1609), however, terms the staminate papaw the male, and the carpellate the female. Even Caesalpinus (1519-1603) and Malpighi (I628-94), who traced the development of the embryo, seem ignorant of the function of the pollen. Grew and Ray at 1east formed conjectures of what we now know to be the truth, but Linneaus and Sachs attribute the demonstmtion of sex in plants to Camerarius (1665-1721). Further experimental confirmation was given by Bradley (1717), Philip Miller (1751), and Linnaeus assumed sexuality in making the sexual organs the basis of his classification. Kolreuter (1733-1806) first studied the artificial production of hybrid plants, and Sprengel (1750-1816) detected the frequent occurrence of dichogamy and the importance of the aid of insects in pollination. After Thomas Andrew Knight, Dean Herbert, and K.F. Gartner had also shown that "Nature abhors perpetual self-fertilisation," Darwin arrived at the conclusion that cross-fertilisation secures a stronger and more numerous progeny. Schleiden in 1837 first pointed out the general protrusion of pollen-tubes by the pollen-grains and their passage into the micropyle; but not till 1846 was it clearly shown by Amici that the egg-cell is formed in the embryo-sac before fertilisation. Among cryptogams, though conjugation in Spirogyra was maintained by Vaucher to be sexual in 1803, and spermatozoids, observed in 1822, had been declared by Unger in 1837 to be male organs, mainly from their resemblance to those of animals, it was not till 1849 that Hofmeister, who did much also to show the absence of spermatozoids in the pollen-tube of the higher plants, gave a complete account of the "alternation of generations" (q.v.) in the higher cryptogams and the fundamental identity of all cases of sexuality as consisting of the fertilisation of a germ-cell by a sperm-cell. It seems that some of the lowest plants (Protophyta) may be destitute of sexuality; whilst in others more highly organised, such as some Saprolegnias and the Basidiomycetes among Fungi, it has been lost by a degeneration-process known as apogamy (g.v.).