AroRI'lIOLOGY 



Fics. 525,526. — Cndtim lalifolium: 525, branches 

 bearing ovulate stroliili; 526, part of o\'Lilatc strobilus. 

 — After Blujie. 



of swimming sperms. In Ephedra 

 a remarkable funnel-shaped jxillen 

 chamber is developed by the break- 

 ing down of the nucellar tissue (fig. 

 528), which extends to the embryo 

 sac and e.xposes the neclcs of the 

 archegonia ; hence in pollination 

 the pollen grains may come to rest 

 in contact with the archegonium 

 necks. In Gnetum the tip of the 

 nucellus is more or less disorgan- 

 ized, and this is the only trace of 

 a pollen chamber (fig. 530); while 

 in Tiiiiihoa there is not e\'en a 

 trace. 



Female gametophyte . — The struc- 

 ture <if the female gametoi>hytc in 

 Gnetales is of great interest, for 

 there is an evident apiproach t<i- pj,, 

 wards the angiosperm condition. 



Ovule. — The ovule has 

 two integuments, the inner 

 one forming a long tubular 

 micropyle, which is a 

 marked feature of the 

 group (figs. 521, 528, 530). 

 The nucellus has the usual 

 gymnosperm feature of a 

 heavy mass of sterile tissue 

 overlying the megaspore 

 mother cell (and later the 

 embryo sac). In all the 

 preceding groups of gymno- 

 sperms, except Coniferales, 

 this overlying tissue is 

 beaked and contains a 

 pollen chamber, a structure 

 associated with the presence 



5 = 7-- 



- Ovulate .strobili of Gnrtiim, 



with Ifebhy beeiJs maturing 



