CYCADALES 



129 



endosperm is differentiated into an endosperm jacket or tapetum as 

 conspicuous as the tapetum of any fern or angiosperm microsporan- 

 gium. In the mature seed the outer fleshy layer remains fresh for 

 a while, and then either dries or decays. All the sporophytic tissue 

 within the stony layer, including the irmer fleshy layer, the nucellus, 

 and the base of the ovule, becomes reduced to a thin dry membrane 

 in which the bundles of the inner vascular system are the most notice- 

 able feature. 



123 124 



Figs. 123-125. — Dioon edule: photographs of ovules after allowing eosin to enter 

 the bundles; fig. 123, vertical view shov\ring 14 bundles; the eosin has spread and 

 exaggerated the size of the outer bundles; fig. 124, photographed after the endosperm 

 and part of the inner fleshy layer had been removed; fig. 125, transverse section; 

 s, stony layer; 0, outer fleshy layer, showing cut ends of bundles of outer vascular 

 system; i, inner fleshy layer with bundles; », inner fleshy layer and fused portion of 

 nucellus; c, endosperm; all X2. — After Chamberlain (46). 



The vascular anatomy of the ovule in its broader features is quite 

 uniform throughout the group. There is an outer set of vascular 

 strands, consisting of a few bundles, that traverses the outer fleshy 

 layer of the integument and extends with little or no branching from 

 the base of the ovule to the micropyle; and an inner set traversing the 

 fleshy layer just within the stony coat, extending to the free portion 

 of the nucellus, branching dichotomously, and often anastomosing. 

 A general view of the two systems of bundles is shown in figs. 123- 

 125. After investigating all the genera except Microcycas and Cera- 

 tozamm, Worsdell (27a) states that two bundles leave the vascular 



