HISTORICAL SKETCH 437 



stigma to the ovule. Schleiden (1837) and Schacht (1850, 1858) took 

 up the study and made a curious misinterpretation: they regarded the 

 ovule as merely a place of incubation for the end of the pollen tube, 

 which they thought entered the ovule and enlarged to form the embryo 

 directly. The work of Amici (1842), Tulasne (1849), and others showed 

 the falsity of this notion, but an acrimonious discussion raged about 

 the subject for a number of years. After W. Hofmeister (1849) and 

 Radlkofer (1856) had followed the process with their characteristic 

 thoroughness, there could remain no doubt concerning the error of 

 Schleiden and Schacht. Hofmeister clearly demonstrated that the 

 embryo arises, as Amici contended, not from the end of the pollen tube, 

 but from an egg contained in the ovule, the egg being stimulated to 

 development by the pollen tube. He was wrong, however, in supposing 

 that the tube did not open and that a fertilizing substance diffused 

 through its wall. 



It was in the algse that the union of the sperm cell with the egg cell 

 (syngamy) was first seen in the case of plants. In 1853 Thbret saw 

 spermatozoids attach themselves to the egg of Fucus, and in 1854 he 

 showed that they are necessary to its development. The actual entrance 

 of the spermatozoid into the egg was first observed in 1856 by Nathanael 

 Pringsheim (1824-1894) in (Edogonium. The fusion of the parental 

 nuclei was seen by Strasburger (1877) in Spirogyra, but he thought they 

 thereupon dissolved. This error was corrected shortly afterward by 

 Schmitz (18796), who was thus the first to show clearly that the central 

 feature of the sexual process in plants is the union of two parental nuclei 

 to form the primary nucleus of the new individual. The demonstration 

 of such a nuclear fusion in a number of algse and fungi soon followed (see 

 Tischler, 1921-1922, p. 462). 



The fusion of the gametic nuclei in bryophytes and pteridophytes was 

 first seen by Kruch (1890) in Riella, and by Campbell (1888) in Pilularia. 

 That the same process occurs in syngamy in the seed plants was demon- 

 strated by Strasburger, who in 1884 described the union of the egg nucleus 

 with a nucleus brought in by the pollen tube (c/. 1877, pp. 56, 76). In 

 1898 and 1899 S. Nawaschin and L. Guignard completed the story by 

 describing "double fertilization," w^herein one male nucleus unites with 

 that of the egg while a second male nucleus unites with the two polar 

 nuclei to form the primary endosperm nucleus. The subsequent work of 

 Strasburger and others on the gymnosperms and angiosperms greatly 

 cleared up the whole matter of syngamy and embryogeny in these plants. 



Animals. — It is probable that the spermatozoon was first seen in 

 1677 by Ludwig Hamm, a pupil of Leeuwenhoek. The credit for the 

 discovery is, however, usually given to Leeuwenhoek, since it was he who 

 brought the matter to the attention of the Royal Society and pursued 

 such studies further. He asserted that the spermatozoa must penetrate 



