Nature and development of plants . F PLANTS 247 surface are also found on the under side of the thallus (, A). These plates curve up around the growing point anddoubtless protect it against drought, in which work they are as-sisted by the mucilage cells or glands. The development of theseglandular cells on the plates, as well as on other parts of thethallus, adapt the plants to the drier terrestrial conditions to whichthey are exposed, as was the case with the mucilaginous walls ofthe Schizomycetes and Zygnematales. (b) Sexual Reproduction of Ricciocarpus.—The gametes areproduced in mo
Nature and development of plants . F PLANTS 247 surface are also found on the under side of the thallus (, A). These plates curve up around the growing point anddoubtless protect it against drought, in which work they are as-sisted by the mucilage cells or glands. The development of theseglandular cells on the plates, as well as on other parts of thethallus, adapt the plants to the drier terrestrial conditions to whichthey are exposed, as was the case with the mucilaginous walls ofthe Schizomycetes and Zygnematales. (b) Sexual Reproduction of Ricciocarpus.—The gametes areproduced in more complex gametangia than we have as yet organs are developed upon the upper surface of the thallusand in some species appear as lines radiating from the center ofthe plant. The male gametangium originates from one of thesuperficial cells of the thallus, which at first continues to dividetransversely after the manner of the vertical plates of chlorophyll-bearing cells (Fig. 181, A). The cells of these vertical plates. Fig. 181. The origin and structure of the male gametangia or an-theridia : A, section of the thallus, showing the apical cell, x, and the earlystages, a, b, in the development of the antheridia. B, older antheridiumwith cells dividing vertically. C, later stage in which the wall cells aredifferentiated. D, mature antheridium of Marchantia, showing the nu-merous cells that develop the male gametes and the wall cells, w. E,greatly enlarged view of a male gamete after discharge from the an-theridium. 248 REPR0DUCT10i\ OF RICCIOCARPUS soon begin to divide vertically and thus form an elliptical massof cells (Fig. 181, B, C). As this growth goes on the outer orwall cells become larger than the others and generally developchlorophyll, while the inner cells divide repeatedly and becomevery numerous with dense granular contents (Fig. 181, D).Each of the latter cells produces a single male gamete that ismotile by means of two cilia (Fig. 181, E). This complex
Size: 1644px × 1520px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublisher, booksubjectplants
