GNETALES 



373 



415 



In Welwitschia the flowers are functionally monosporangiate and 

 dioecious, but the staminate flowers are structurally bisporangiate 

 (figs. 415, 416). They are borne in 

 the axils of broad and closely over- 

 lapping bracts, whose decussating 

 pairs form a conifer-hke strobilus 

 (figs. 417, 418). These strobili are 

 produced upon branching axes which 

 arise from the crown above the foliage 

 leaves, or rarely beneath them. Pear- 

 son (20), from a field study of Wel- 

 witschia, states that it is probably 

 partially if not wholly pollinated by 

 insects, a statement which finds addi- 

 tional confirmation in the fact that 

 just below the anthers there are glan- 

 dular protuberances which, in sections, 

 may be interpreted as nectaries (fig. 

 415. 0- 



The staminate flower consists of two 

 decussate pairs of free bracts, within 

 which there is a whorl of six (rarely five 

 or four) monadelphous stamens, each 

 of which bears a terminal peltate group 

 of three sporangia arranged in an 

 approximately circular synangium. In 

 the center there is a single sterile ovule 

 whose projecting micropylar tube is 

 spirally coiled and ends in a broad 

 flaring expansion (figs. 415, 416). It 

 is very evident that the immediate 

 ancestors of Welwitschia had bispo- 

 rangiate flowers, a feature completely 

 ehminated from most of the gymno- 

 sperms, if they ever possessed it. The 

 only other g)minosperms that possess 

 it are the Bennettitales, and they are 



6 J « 



416 



Figs. 415, 416. — Welwitschia 

 miraUUs: fig. 415, longitudinal 

 section of the flower; p, bracts of 

 perianth; s, trilocular anther; t, 

 protuberance on the inner face of 

 the stamen tube; i, inner integu- 

 ment, ending above in the ex- 

 panded "stigma"; n, nucellus of 

 sterile ovule; b, bract from the axil 

 of which the flower arises; X30; 

 fig. 416, diagram of transverse 

 section of the flower at the level 

 of i in the preceding figure; -)-, 

 axis of cone. 



