326 



BOTANY 



are more nearly related to the Pteridophytes than they are to the 

 Angiosperms. The recent discovery of sperniatozoids in several of 

 the lower forms has emphasized the near relation of the Gymno- 

 sperms to the other Archegoniates, with which perhaps they should 

 be included. In number, the Gyinnosperrns are very much inferior 

 to the more recent and specialized Angiosperms. They nevertheless 

 include some of the largest and most important of all plants. The 

 prevailing modern Gymnosperms are the Conifers, especially well 

 developed upon the Pacific slope of North America. The Cycads are 

 mostly tropical forms, much inferior in size and numbers to the Coni- 

 fers. The Gnetales comprise a small number of plants of doubtful 

 affinities. 



.en 



Fio. 289. A-C, Cycas revoluta. A, young leaf from a small plant, showing the 

 incurved pinnae. B, cross-section of the petiole (X6); fb, vascular bundles ; 

 m, gum-passage. C, vascular bundle of petiole (X 175) ; en, endodermis; s, sieve- 

 tubes; t, tracheids. D, cross-section of the peduncle of the cone of Zamia 

 integrifolia (X 2). 



Classification of Gymnosperms. The existing Gymnosperms may 

 be divided into four orders Cycadales, Ginkgoales, Coniferse, and 

 Gnetales. To these may be added two extinct orders, Cycado-filices 

 and Cordaitese. 



Order I. Cycadales 



The lowest of the existing seed-bearing plants, with the possible 

 exception of Ginkgo, are the Cycads, comprising about seventy -five 

 species, for the most part confined to the Tropics. A single species, 

 Zamia integrifolia, occurs in Florida, and Cycas revoluta (PI. IV) 

 reaches beyond the northern tropic in Japan. 



