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The Anatomy and Morphology of the Leaves and Injiorescences of 



Welwitschia mirabilis. 



By Miss M. G. Sykes. 



(Communicated by Prof. A. C. Seward, F.R.S. Received May 28, — Read 



June 30, 1910.) 



(Abstract.) 



The paper deals with the anatomy of the leaves and inflorescences of 

 Welwitschia, and with certain theoretical questions which arose during their 

 examination. Cotyledons, leaves, bracts, and flowers each receive two 

 bundles when young, though in the adult leaf numerous additional bundles 

 are intercalated. 



The transfusion tissue, which more or less surrounds the bundles in all 

 the foliar members, is developed in the pericycle ; in the bracts, and to a 

 smaller extent in the old leaves, there is a further development of transfusion 

 tissue from the cortical parenchyma. This second type of transfusion 

 tissue recalls that of Cycas, and the presence of centripetal xylem at the base 

 of the cotyledonary bundles is another character suggesting z-elatiouship with 

 the Cycads. 



The structure of the peduncles, cone-axis, cone-bracts, and flowers is 

 essentially similar in both male and female inflorescences, which are therefore 

 regarded as homologous. 



In the naked inflorescence axes the formation of inversely orientated 

 bundles and the presence of xylem elements in a position internal to the 

 protoxylem again recalls the Cycads. Below the points of branching a series 

 of elongated and waved bands of vascular tissue are formed, each consisting 

 of a band of normally orientated xylem and phloem with an inversely 

 orientated band on its outer edge. The structure at this level is compared 

 with Colpoxylon and others of the Medullosete. 



The two bundles which supply the female flower stalk each branch to form 

 three ; the central bundle of each trio passes out into the outer integument^ 

 while the remaining four give rise to the perinucellary ring, which dies out 

 at the level at which the inner integument becomes free. From the position 

 of this inner system it appears clear that it belongs to the inner integu- 

 ment. 



In the male flower axis additional bundles are formed to supply the 

 stamens, but the branching of the bundle is much as in the female. A 



