. Nature and development of plants. Botany. DEVELOPMENT OF PLANTS 369 new departure. The microspores which have already begun to germinate when discharged from their sporangia are carried by the wind to the megasporophylls which are sHghtly spread apart at this time, permitting the microspores to rattle down to the megasporangia. The microspores fall into the micropyle either by reason of the position and construction of the megasporangia, which may be so placed that the spores naturally roll down into the micropyle, or the microspores may be drawn through the micropyle by mucilaginous excreti
. Nature and development of plants. Botany. DEVELOPMENT OF PLANTS 369 new departure. The microspores which have already begun to germinate when discharged from their sporangia are carried by the wind to the megasporophylls which are sHghtly spread apart at this time, permitting the microspores to rattle down to the megasporangia. The microspores fall into the micropyle either by reason of the position and construction of the megasporangia, which may be so placed that the spores naturally roll down into the micropyle, or the microspores may be drawn through the micropyle by mucilaginous excretions as in the cycads. The. Fig. 254. Male gametophyte of the pine: 6, section of microspore, show- ing the two air sacs, s, formed by the lifting up of the outer wall of the spore. 8, stage of germination of the spore at time of discharge from its sporangium —t, tube cell; a, antheridial cell, above which are seen two black lines, the remains of cells formed by earlier division of the nucleus of the microspore. 9, continuation of germination of the microspore after reaching the mega- sporangium—t, tube cell forming a branching tube that disorganizes and ab- sorbs the cells of the megasporangium. The antheridial cell (a) of 8 has divided into a wall cell, w, and a body cell, b. 10, end of tube cell as it ap- proaches the female gamete—m, m, male gametes. The nuclei of the tube cell and wall cell are also seen (somewhat disorganized) in the end of the tube. —After Coulter and Chamberlain. early stages in the germination of the microspore are essentially as in Cycas, though generally more reduced. The microspore on reaching the megasporangium has germinated, forming a tube 24. 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 Curtis, Carlton Clarence, 1864-1945. New York, H. Holt
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Keywords: ., bookcentury1900, bookdecade1910, bookpublisher, booksubjectbotany
