. Heredity and evolution in plants. Heredity; Plants. 126 HEREDITY AND EVOLUTION IN PLANTS 101. Evidence from Comparative Ontogeny.—In zool- ogy, evidence of the course of evolution is also seen in the recapitulation of the characters of lower forms in the em- bryogeny of higher forms. This is often referred to as von Baer's law. Evidence of that nature is less striking and less common in plants. It is found, however, in a com- parison of the young or embryonic stage of the sporophyte of the higher liverwort, Marchantia, with the mature. Fig. 64.—The apical cell in the stem apex in various phy
. Heredity and evolution in plants. Heredity; Plants. 126 HEREDITY AND EVOLUTION IN PLANTS 101. Evidence from Comparative Ontogeny.—In zool- ogy, evidence of the course of evolution is also seen in the recapitulation of the characters of lower forms in the em- bryogeny of higher forms. This is often referred to as von Baer's law. Evidence of that nature is less striking and less common in plants. It is found, however, in a com- parison of the young or embryonic stage of the sporophyte of the higher liverwort, Marchantia, with the mature. Fig. 64.—The apical cell in the stem apex in various phyla, from Bryophytes to Gymnosperms. A, acrogynous liverwort (Notothylus orbicularis); B & C, eusporangiate ferns {B, Maraitia Douglasii, C, Ophioglossum pendulum); D & E, homosporous leptosporangiate ferns (D, Osmunda Claytoniana, E, Adlanlum emarginatum, representing Polypodi- ales); F, heterosporous leptosporangiate fern {Marsilia vestita); G, a horsetail (Calamophyte) (.Equisetum ielamateia); H, a late gymnosperm {Pinus Laricio). {A-G redrawn from Campbell, H from Buchholz). sporophyte of the lower Uverwort Riccia (Fig. 65). The latter consists almost entirely of "fertile" {, reproduc- tive) cells. As we pass to more highly organized forms, such as Marchantia, the relative amount of vegetative tissue gradually increases by a progressive sterilization^ of fertile tissue. This progressive sterihzation is repeated in the ontogeny of the sporophytes of the higher forms. The thread-like, green protonema of mosses is often in- 'See foot-note, p. 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 Gager, C. Stuart (Charles Stuart), 1872-1943. Philadelphia, P. Blakiston's Son & Co.
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