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A TEXTBOOK OF THEORETICAL BOTANY 



Fig. 762.- — Comparison of vessel perforations in Ephedra and Giietum. A and B, Ephedra 

 monostachya, showing the relationship between vessel perforations and bordered 

 pits. Vessel plate in surface view and section. C and D, Gnetum gnemoii. Vessel 

 plate from the root of a seedling showing correspondence with the Ephedra type. 

 E to H, Gnetujti molucceuse. Series of stages from the node of a seedling showing 

 transition from E, Ephedra type, to H, Gnetum type. {After Thompson.) 



The Female Flower. 



The female flower is simply an ovule, consisting of a nucellus (a mega- 

 sporangium) surrounded by three envelopes (Fig. 763). The inner is pre- 

 sumably an integument, comparable to that in other Gymnosperms, except 

 that, as in Ephedra, it elongates into a micropylar tube. The morphological 

 nature of the two outer coverings has been much discussed without any final 



