FURTHER STUDIES ON GYMNOSPERMS. 



219 



are exposed on the outer surface. All the plants of the great group to 



which the pine belongs have 



naked seeds. For this reason 



the name " gymnosperms " 



has been given to this great 



group. 



438. Classification of gymno- 

 sperms. — The gingko tree has 

 until recently been placed with 

 the pines, yew, etc., in the class 

 conifertz, but the discovery of 

 the spermatozoids in the pollen 

 tube suggests that it is not 

 closely allied with the coniferse, 

 and that it represents a class 

 coordinate with them. Engler arranges the living gymnosperms as follows : 



Fig. 288. 

 Spermatozoids of 

 zamia in pollen tube 

 J>g, pollen grain; a, a, 

 spermatozoids. (After 

 Webber.) 



Fig. 289. 

 Spermatozoid of zamia 

 showing spiral row of 

 cilia. (After -Webber.) 



Class 1. Cycadales ; family Cycadaceae. Cycas, zamia, etc. 

 Class 2. Gingkoales ; family Gingkoacese. Gingko. 



Class 3. Coniferse ; family 1. Taxacese. Taxus, the common yew in the 

 eastern United States, and Torreya, in the 

 western United States, are examples, 

 family 2. Pinacese. Araucaria (redwood of California), 

 firs, spruces, pines, cedars, cypress, etc. 

 Class 4. Gnetales. Welwitschia mirabilis, deserts of southwest Africa ; 

 Ephedra, deserts of the Mediterranean and of West 

 Asia. Gnetum, climbers (Lianas), from tropical Asia 

 and America. 



