462 GNETALES [CH. 



furnishes a point of contact with the Araucarineae ; rims of Sanio 

 occur and xylem-parenchyma is abundant; the medullary rays 

 are multiseriate as in Dicotyledons. The bast on the other hand 

 is essentially gymnospermous. The occasional occurrence of spiral 

 bands in the tracheids and the presence of lignified trabeculae in 

 the xylem-elements are other Coniferous traits. The leaf-trace is 

 double, a feature met with in Agathis as well as in recent Cycads 

 but not in the Bennettitales. The anatomy of seedlings affords 

 further indications of resemblance to Araucaria and the Podocarps 1 . 

 It would seem, then, that the case for a relationship between the 

 Gnetales and the Bennettitales founded on the facts of floral 

 morphology does not derive support from the anatomical features 

 of the most primitive genus of the group. 



Gnetum. 



Small trees or climbers with long and slender stems ; the inter- 

 nodes, sometimes reaching a length of 15 cm., bear pairs of ovate- 

 oblong or lanceolate-acuminate leaves 11 18 cm. long by 4 7 cm. 

 broad. The leaves 2 agree in form and venation with those of 

 many Dicotyledons and could not be distinguished from them in 

 a fossil state. The epidermal cells have undulate walls. The 

 flowers are in spikes; at each node two fused bracts form a cupular 

 structure in the axil of which the male or female flowers are borne 

 on an annular swelling. The male flowers 3 are in 3 5 whorls: 

 each consists of an envelope of two coherent leaves enclosing a 

 central column, as in Ephedra, which bears at the apex one, two, 

 or rarely four unilocular sporangia or reduced synangia. The 

 antherophore eventually elongates and pushes the anthers through 

 an aperture at the summit of the floral envelope 4 . In appearance 

 the antherophore of Gnetum approaches most closely to the stamen 

 of an Angiosperm. The female flowers 5 occur in a single series, 

 5 8 in a whorl; each consists of an ovule surrounded by three 

 envelopes; the outermost is coloured and succulent, the middle 

 envelope or outer integument is differentiated after fertilisation 

 into an inner sclerotesta and an outer sarcotesta, while the inner- 

 most covering is prolonged as a micropylar tube. There are no 



1 Hill and de Fraine (10) p. 329. 2 Karsten (93); Lotsy (11) p. 347, fig. 209. 



3 Caporn (16). 4 See also Pearson (15). 



5 Thoday (Sykes) (11); Lignier and Tison (13). See also Pearson (17). 





