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 



