318 PKACTICAL BOTANY 



immense cones (Fig. 263), tlie largest cone known in the plant 

 kingdom being found in this family. 



In details of structure of the vegetative body of cycads, 

 and in their reproductive structures and processes, they are 

 of great interest and importance to special students of botany. 

 For our present purposes, however, there should merely be 

 noted (1) the fern-like appearance of cycads; (2) the stem 

 and leaves, which resemble the large and abundant plants 

 of the Carboniferous age ; (3) the fact that in some cycads 

 (^Cycas revoluta) the carpels are leaf -like, with sporangia at 

 the margins as in some ferns ; (4) that the megaspore, which 

 is scarcely inclosed within- the ovule, develops a female game- 

 top hyte, which bears several to many archegonia ; (5) that the 

 male gametophyte produces usually two but in some forms it 

 produces several true sperms, provided abundantly with cilia 

 and able to swim about with great vigor in the pollen tube. 

 These facts show that in many respects cycads are more like 

 ferns than are the pines. They are more like ancient forms of 

 plants than like present-day ferns, and in ancestry are very old. 



There were formerly many species of plants to which our 

 present cycads are related, but most of them are dead and 

 now represented only by their fossils. The cycads are there- 

 fore looked upon as the slowly disappearing remnants of a 

 once abundant type of plant life. 



290. Other groups. The Gnetales are now represented by but 

 three very different genera, the remnants of once abundant 

 and successful plants, but too highly specialized for use in this 

 discussion. 



The "maidenhair tree" (^Crhikr/o) — a tree with leaves 

 (Fig. 264) that suggest the maidenhair fern — is becoming 

 somewhat generally planted as a shade and ornamental tree. 

 It is the only living species of a former abundant group 

 (^GrinJcffoales") of gymnosperms. 



291. Gymnosperms of past ages. It has been stated that 

 pteridophytes were the dominant plants in the Carboniferous 

 age. Fossils of ancestral seed plants also Avere formed during 



