332 Welwitschia. 



bündle iu the stele and sometimes tlie two traces arise together from 

 the Stele and become free from each other later. 



In Onetum the bundles whicli supply the flowers and bracts have 

 their origin in a common bündle which runs for some way in the 

 cortex before branching. Such an arraugement Supports the hypothesis 

 that each „flower" represents a sorus which was originally borne on 

 the bract. 



The main difficulty in the alliance of Wehvitschia with the Cycads 

 which lies in the apparently axillaiy position of the flower in Wehritschia 

 may perhaps be not insurmountable: it has been above suggested that 

 this Position may be a secondary development. In Oijcas the seed is 

 probably derived from a sorus consisting of only one fertile sporangium 

 and is borne on the unmodified leaf, in the other Cycads the female sorus 

 is similarly constructed and two of them are commonly associated with 

 only a small specialised segment of the leaf, the ovuliferous scale: in 

 JVehvitschia it may be, that the female sorus, which has usually been 

 termed the female flower, is derived exactly as in the latter group of 

 genera, the bract being then equivalent to the specialised segment or 

 ovuliferous scale. The scale must then be regarded as secondarily sepa- 

 rated from the Single sorus in connection with it. 



The male flow^ers are rather more difflcult to homologise; in the 

 Cycads the male sporophyll bears a number of sori. It appears likely 

 tliat Welicitschla is also derived from a form in w^hich the fertile segment 

 bore several sori, and the fertile segment is now metamorphosed into 

 the bract, while the aggregation of placentae or sporangiophores bearing 

 the several sori have given rise to the male „flower", this consists of a 

 central sorus of one aborted macrosporangium and six peripheral stalked 

 synangia, probably each originally equivalent to a sorus (sehr einleuchtend 

 ist dies nicht, wo treifen wir bei Cycadeen Makro- und Mikrosporangien 

 in einem Sorus an?). The bracteoles surrounding the flow^er may be 

 perhaps compared with the emergences found surrounding the sorus of 

 the Schheaceae ; on the other band they may be derived from sterilised 

 sporangiophores or even as a rudimentary eucasement such as that from 

 which the outer integument of the ovule has been derived. It does not 

 seem to me possible to regard them as the equivalent of bracts and at 

 present I think it would be rash to term them a perianth." 



Schließlich meint Miss Sykes, daß die Gnetalen von den Cycadalen 

 abgeleitet werden müssen, und zwar irgendwo bevor die Bennetiiten sich 

 abzweigen, also etwa so: 



Gnetales 



Cycadales 



Wie gesagt, scheint mir die ARBERsche Auffassung die richtigere 

 und ich schließe also : 



1) 6 und ? Blüte von Wehvitschia sind homologe Gebilde; | 



2) beide sind von einem bisporangiaten Pro-anthostrobilus herzu- 

 leiten, sind also dem Bennettites-'&iTohilw^ homolog; 



