. Heredity and evolution in plants. Heredity; Plants. THE EVOLUTION OF PLANTS ^33 possible steps in the evolution of the sporophyte may, on this theory, be tabulated as follows:' 1. Sterilization of fertile tissue. 2. Localization of spore-production in sporangia. 3- Origination of lateral organs (leaves), and of roots. 4. Development of heterospory. 5- Introduction of fertihzation by the pollen-tube (siphonogamy). 6. Assumption of the^ 3P0E0PHYTE Fig. 67.—Diagram illustrating the gradual change in the relative promi- nence of the gametophytic and sporophytic phases in the life-cy
. Heredity and evolution in plants. Heredity; Plants. THE EVOLUTION OF PLANTS ^33 possible steps in the evolution of the sporophyte may, on this theory, be tabulated as follows:' 1. Sterilization of fertile tissue. 2. Localization of spore-production in sporangia. 3- Origination of lateral organs (leaves), and of roots. 4. Development of heterospory. 5- Introduction of fertihzation by the pollen-tube (siphonogamy). 6. Assumption of the^ 3P0E0PHYTE Fig. 67.—Diagram illustrating the gradual change in the relative promi- nence of the gametophytic and sporophytic phases in the life-cycle of plants during their evolution from the primitive algje (at the left) to the modern seed-bearing plants (at the right). 108. Second Hypothesis.—In a discussion of Bower's theory, Tansley,^ considers it "a priori in the highest degree unlikely that so fundamentally important an organ as the foliage leaf of the vascular plant appeared in descent as an ' enation' from the surface of a cylindrical body of different morphological nature," and states that "there is no well established case of any such origin of an organ of the importance and with the potentialities of the leaf in the evolutionary history of the plant ; He also calls attention to the fact that the sporophyte (sporo- gonium) of mosses and liverworts has never been known to produce by enation or otherwise, any structure resembling ' Following F. O. Bower. 2 New Phytologist 7:177-129. April and May, 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.
Size: 2705px × 924px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, booksubjectplants, bookyear1920
