SPERMATOPHYTA 321 



to the leaf, two leaf traces girdle the cortex in opposite directions, each 

 passing about halfway around the stem in going from their point of origin 



to the leaf. 



The cones of the Bennettitales, each occurring in the axil of a leaf, are 

 borne laterally along the stem. In Macrozamia and Encephalartos the 

 cones are also lateral and axillary, although arising close to the stem tip. 



Fig. 269. Cross section of the stem of Zamia fioridatia, showing large pith, thin vascular 

 cylinder, and thick cortex with portions of the girdling leaf traces, X4. 



In the other genera the original apical meristem is used up in the forma- 

 tion of a cone, and a new meristem appears at its base. This produces a 

 branch that soon becomes erect and gives rise to a new crown of leaves. 

 Thus the first cone produced by a plant is terminal, but all the rest are 

 morphologically lateral, although borne at the summit of the stem. All 

 cycads are monosporangiate and dioecious. 



Staminate Strobilus. The staminate strobili are usually borne singly, 

 but in Zamia, Macrozamia, and Encephalartos several or many may occur 

 together (Fig. 2705). They are composed of an axis bearing many spi- 

 rally aa-ranged microsporophylls (stamens) that are always compactly 

 organized. The microsporophylls are not at all leaf-like, but are narrow 

 below and broadened above into a sterile tip (Fig. 271). The microspo- 

 rangia are abaxial and borne in sori of two to five, but not in synangia. 

 They range in number from over a thousand on each sporophyll in Cycas 

 to a comparatively few in Zamia. Their development is eusporangiate, 

 the initials being hypodermal in origin rather than epidermal as in the 



