CYCADALES 



97 



in E. cafer. A bud coming from a wound in an old E. altensteinii 

 plant shows typically spiny leaves. 



The leaves of all the cycads have a strongly xerophytic structure 

 (fig. 89). The cells of the epidermis have thick walls and are heavily 

 cutinized. The stomata are sunken and are mostly confined to the 

 under surface, except in Bowenia and Macrozamia. In Microcycas 

 there is not much thickening of the hypodermal cells, except above 

 and below the bundles and near the margins of the leaflets ; in Macro- 



FiG. 89. — Dioon edule: transverse section of part of leaflet, c, cuticle; e, epidermis; 

 h, hypodermis; p, palisade; s, suberized cell. — From Chamberlain, The Living Cy- 

 cads"" (University of Chicago Press) . 



zamia moorei the hypodermal cells are thick walled throughout; and 

 in Encephalartos altensteinii the thick-walled hypodermal region is 

 several cells thick. 



There is usually a well-marked palisade layer and a more or less 

 spongy parenchyma beneath. The bundles are usually surrounded by 

 thick-walled cells, and such cells often extend from the bundle to the 

 hypodermal cells above and below. Many of the thick- walled tra- 

 cheids around the bundles, and nearly all thick-walled tracheids scat- 

 tered through the thin walled cells between bundles, are bast fibers. 



