no GYMNOSPERMS 



chromosomes, which, of course, takes place during the formation of 

 megasporcs from the megaspore mother cell, has not yet been de- 

 scribed, but counts in microsporogenesis and in other phases of the 

 Ufe-history have constantly shown that the x and 2x numbers are 

 12 and 24. 



As the megaspore germinates, the cells next to the developing fe- 

 male gametophyte become differentiated into a layer of "spongy 

 tissue," looking like sporogenous tissue on account of the dense cell 



\ 



Fio. 102. — Dioon edtilc: A, transverse section of ovule near the middle; B, inner 

 vascular system, treated with eosin and photographed after the female gametophyte 

 and part of the inner fleshy layer had been removed; C, ovule photographed from above; 

 0, outer bundles (the eosin has diffused some in A, and considerably in C); m, micro- 

 pyle; s, stony layer; /, inner vascular system; p, basal papilla; e, female gametophyte; 

 n, inner fleshy layer; X2. — After Chamberlain.'"* 



contents. This layer nourishes the gametophyte in early stages, then 

 weakens and finally becomes almost indistinguishable. Such a layer, 

 very highly developed in cycads, is prevalent in gymnosperms. 



The male strobtliis (fig. 106). — The male, or microsporangiate, 

 strobilus is not so large as the female and there are no leafy sporo- 

 j:)hylls like the megasporophylls of Cycas revolula. All of the strobili 

 are compact cones, even in Cycas. Occasionally there is a slight pro- 

 liferation of the axis, producing a few much reduced leaves, but the 

 cone ripens, dies, and any further development comes from a new 

 meristem. This applies to stems bearing a single terminal cone, as in 

 Dioon and many others. When cones are axillary, as in Macrozamia 



