CHAPTER Xxn 



The Cycads and Certain Extinct Seed-bearing Plants 



A GROUP may now be considered which, although portrajdng 

 many of the characteristics of Flowering Plants, nevertheless 

 shows several features reminiscent of Ferns. The plants in 

 question are the Cycads, which have a wide distribution in the 

 tropical regions of America, South Africa, Eastern Asia, and 

 Australia, though most of the genera have a very restricted 

 range. Fossil records show the group to be a very ancient one 

 that played a particularly important part during the Mesozoic 

 period, the present-day representatives appearing merely as 

 relics. The Sago-palm {Cycas revolnta) is in most respects 

 typical of the living forms. 



Most Cycads (Fig. 183) have the appearance of Palms or 

 Tree Ferns, the often huge pinnate leaves forming a crown at 

 the top of the partly subterranean and tuberous, or overground 

 and columnar, stems ; in the latter case the stems may attain 

 a height of sixty feet. The trunk is rarely branched, and, in 

 the older portion, its entire surface is covered with an armour 

 formed by the persistent bases of the leaves of previous seasons. 

 Fresh crops of leaves are produced at intervals, the outer ones 

 being modified to form protective bud-scales. In some of the 

 genera the unfolding leaves exhibit a spiral inrolling of the 

 pinnae [e.g. Cycas, Fig. 184), or of the midrib, similar to that 

 characteristic of Ferns. Other resemblances to this group are 

 to be found in the forked veining of the blades (Fig. 185, E) 

 and in the structure of the petiole. The numerous vascular 

 strands of the latter have the protoxylem embedded within the 

 metaxylem, a feature especially characteristic of Ferns (cf. p. 293 

 and Fig. 160, P.xy.), whereas in the vast majority of the Seed- 



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