CHAPTER XIII 

 CONIFEROPHYTES— CONIFERALES— Co«/mwe(/ 



THE MALE GAMETOPHYTE 



The microspore is the first cell of the male gametophyte. All of 

 the four microspores produced by a microspore mother-cell seem 

 equally vigorous and capable of completing the entire life-history, 

 and nearly all of them germinate and complete more or less of the 

 life-history while still inclosed in the microsporangium. In some 

 species of Cupressus and Juniperus the microspore is shed in the 

 uninucleate condition; but, in such cases, a division occurs soon after 

 reaching the nucellus, before the pollen tube begins to be formed. In 

 these cases there are no prothalUal cells, the first division giving rise 

 to a generative cell and a tube nucleus. Consequently, the micro- 

 spore is the antheridial initial. 



In this more or less advanced stage of development, the micro- 

 spores, or pollen grains, are shed. The whole order is wind-pollinated. 

 In spite of occasional claims, it is very doubtful whether there is a 

 single case of insect pollination in any gymnosperm. Pollen is shed 

 in prodigious quantities. In pine forests, lumbermen speak of "sul- 

 phur showers." No doubt there are millions of pollen grains in a 

 cone of Araucaria hidwilli, and Burlingame^'' estimated the output 

 in A. braziliensis as high as a billion. In any case, the output is im- 

 mense, and nearly all of the pollen grains die. Very few reach a 

 nucellus, where they may continue their development and form 

 pollen tubes. 



The microspore always has two spore coats, exine and intine, 

 which vary in their comparative thickness. Usually, the exine is 

 thicker; but in some cases, like Araucaria hidunlli, the intine may be 

 more than twice as thick as the exine. When the pollen is winged, 

 the wings are formed from the exine. StrasburgerS'^ believed that 

 the wings arose from a splitting of the exine. Dr. Margaret 

 Ferguson"'' decided that they originate by a separation of the exine 



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