136 TEXTBOOK OF BOTANY 



back to very ancient ferns that were related to some tropical ferns of 

 the present time. The modem cycads are the survivors of what was 

 once a much larger group. WhUe there can be little doubt that the 

 conifers, including the pine, have also come from fern-like ancestors, 

 their descent is not yet so well known as is that of the cycads. Another 

 gymnosperm is Ginkgo, the " maidenhair tree " of China and Japan, 

 many specimens of which are to be found in Europe and America. 

 This also is a survivor of what was once a large group. The cycads 

 and Ginkgo differ from all other seed plants (including the conifers) 

 in the fact that their male gametes have vibrating hairs and so can 

 swim about like those of the fern and the moss. However, the cycads 

 and Ginkgo, like the pine, also have a pollen tube, which furnishes a 

 path for the antherozoids to reach the eggs. 



