SPERMATOPHYTES : GYMNOSPERMS 



189 



extinct ones. The groups differ so widely from one an- 

 other in habit as to show that Gynmosperms can be very 

 much diversified. They are all woody forms, but they may 

 be trailing or straggling 

 shrubs, gigantic trees, or 

 high-climbing vines ; and 

 their leaves may be nee- 

 dle-like, broad, or "fern- 

 like." For our purpose it 

 will be only necessary to 

 define the two most prom- 

 inent groups. 



105. Cycads. — Cycads 

 are tropical, fern - like 

 forms, with large branched 

 (compound) leaves. The 

 stem is either a columnar 

 shaft crowned with a ro- 

 sette of great branching 

 leaves, with the general 

 habit of tree-ferns and 

 palms (Figs. 155, 156) ; 

 or they are like great tu- 

 bers, crowned in the same 

 way. In ancient times 

 (the Mesozoic) they were 

 very abundant, forming 

 a conspicuous feature of 

 the vegetation, but now 

 they are represented only 

 by about eighty forms 

 scattered through both 

 the oriental and occiden- 

 tal tropics. 



They are very fern- 

 like in structure as well 

 31 



Fig. 159. The giant redwood (Sequoia gi- 

 gantea) of California: the relative size 

 is indicated by the figure of a man stand- 

 ing at the right.— After Williamson. 



