(TCADALES 



inder, and the mucilage canals passing on to join the cortical 

 canal system. 



The xylem elements are of the general Gymnosperm charac- 

 ter. They are all tracheids, the first formed being spiral in 

 type and the later scalariform; while in the tracheids of the 

 secondary xylem the characteristic bordered pits appear, or 

 a mixture of scalariform and reticulate thickenings may be 

 developed, as in Zamia. Mucilage ducts are common in all 

 organs, and the pith is also remarkably rich in stored starch. 



THE LEAF 



The alternation of rosettes of scale leaves and foliage leaves 

 near the apex of the stem is a conspicuous feature. According 

 to Goebel, every year or every other year a rosette of foliage 

 leaves is expanded, in the center of which is a terminal bud 



5. Cross section of a leaf of 



revoluta. 



invested by numerous scale leaves under whose protection a new 

 rosette of foliage leaves slowly develops (Fig. 1). In the green- 

 house material we have examined there are no such regular peri- 

 ods of unfolding. The alternation is still more striking when 

 sporophylls are included, scale leaves, foliage leaves, and sporo- 

 phylls being the order of succession. 



The scale leaves are brown and dry. The foliage leaves are 

 pinnate and leathery, and generally develop expanded, but in 

 2 



