. Practical botany. Botany. GYMNOSPERMS 307. borne microsporangia. In the microsporangia, microspores or pollen are formed. They have peculiar wing-like outgrowths (Fig. 254), which help to buoy them upon the wind. The pollen is shed in great quantities and may be carried long distances by currents of air. Indeed, so extensive are the showers of microspores of pines at times, that ignorant people have im- agined that they were showers of sulphur from some distant active volcano. Early names and more recent ones, all of which are still used for the structures of the staminate cone, are sta- men
. Practical botany. Botany. GYMNOSPERMS 307. borne microsporangia. In the microsporangia, microspores or pollen are formed. They have peculiar wing-like outgrowths (Fig. 254), which help to buoy them upon the wind. The pollen is shed in great quantities and may be carried long distances by currents of air. Indeed, so extensive are the showers of microspores of pines at times, that ignorant people have im- agined that they were showers of sulphur from some distant active volcano. Early names and more recent ones, all of which are still used for the structures of the staminate cone, are sta- men for microsporophyll, pollen or pollen grains for microspores, pollen sacs for microsporangia, and staminate flower for the strobilus or cone, which bears the microsporophylls. 284. Pollination. The pollen, or microspores must be car- ried to the seed cone and properly placed before they can develop. The proper placing of pollen is called pollination (Chapter VIII). In pines, young seed cones stand upright and open (Fig. 248) at the time pollen is being shed. If pollen grains chance to come into the seed cones, they slide down upon the leaf-like parts to the base where the sporangia are borne. There by means of a sticky secretion they are caused to adhere to the tip of the mega- sporangium, and pollination is completed. Obviously, if wind- pollinated plants are to be successful, there must be enor- mous quantities of very light pollen, and ovule-bearing cones must be open to catch pollen that chances to fall upon them. Fig. 253. A few of the stamens and pollen sacs from a staminate cone of the pine Somewhat enlarged Fig. 254. An enlarged pollen grain of the pine Much magnified. 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 Bergen, Joseph Y. (Joseph Young), 1851-1917; Caldwell, Otis William, 1869- joint aut
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