460 GNETALES [CH. 



Welwitschia, in some species of Gnetum, and occasionally in 

 Ephedra. The seeds are albuminous and the embryos have two 

 cotyledons. Archegonia are produced in the female prothallus of 

 Ephedra while in Gnetum and Welwitschia these organs are repre- 

 sented by single cells as in the Angiosperms or by nuclei. 



Ephedra^ has a wide distribution in the warm temperate regions 

 of the northern hemisphere: in America it occurs on both sides 

 of the equator and from the Mediterranean region it reaches to 

 Brittany in the west and North Africa in the south. Gnetiu 

 extends both east and west in the tropics: Gnetum scandens is a 

 widely spread Asiatic species, and the genus occurs in Angola and 

 in some other parts of Africa. Welwitschia is confined to a littoral 

 strip of desert in extra-tropical South Africa from 14 S. to 23 S 

 and has not been found more than 50 miles from the coast. 







Ephedra. 



Shrubs, in some species with climbing branches, characterised 

 by an Equisetum-like habit of the younger shoots which form long- 

 jointed and slightly fluted branches bearing whorls of two or 

 sometimes three, scaly, concrescent leaves. In rare cases, e.g. 

 Ephedra altissima, the leaves may reach 3 cm. in length and a 

 breadth of 1 1-5 mm. Monoecious or dioecious; flowers uni- 

 sexual; bisexual inflorescences are recorded in E. campylopoda 2 . 

 The female flowers occur in strobili on a dichasially branched 

 inflorescence; each strobilus consists of three pairs of bracts, in 

 some species the bracts are more numerous. There is generally a 

 single ovule in E. altissima, but in most species there are two or as 

 many as six ovules in a single strobilus. The ovules are enclosed 

 by two envelopes regarded by some authors as a perianth and an 

 integument and by others as two integuments. In E. distachya, as 

 described by Mrs Thoday and Miss Berridge 3 , two vascular bundles 

 supply the outer envelope (outer integument) one running up each 

 angle of the flattened side of the flower. The thin inner integument 

 becomes free from the nucellus at a distance of two-thirds its 

 length and projects beyond the outer envelope as a long style-like 

 micropylar tube. A ring of bundles runs a short distance up the 

 inner integument but ends low down in a mass of transfusion- 



1 Stapf (89). 2 Wettstein (11) p. 417. 3 Thoday (Sykes) and Berridge (12). 



