16 
DR R. C. DAVIE ON 
of the recent papers deal mainly with the centripetal and centrifugal developments 
of the xylem in the individual strands. In many Cycads, as is well known, the 
outline of the leaf-trace is very elaborate. It has been found that in most of the 
genera the pinna-traces are simple and simply developed ( cf. Prantl, ’89). 
Stangeria par adoxa, T. Moore. 
The genus with the simplest leaf is Stangeria. Stangeria par adoxa, T. Moore, 
has a rather short leaf bearing a few simple pinnae at considerable distances from 
one another. At the base of the petiole the leaf-trace has the outline shown in 
text-fig. 9a. There the adaxial face of the petiole is lined by several small 
strands. As they pass up the petiole they move right and left and take up their 
positions on the adaxial corners of the antero-posterior flanks of the leaf-trace, 
sometimes fusing among themselves, sometimes with the strands at the corners of 
/ 
the petiolar system. A small strand remains for some time in the median position 
on the adaxial face of the petiole (text-fig. %). It comes from the series shown 
on the adaxial face in text-fig. 9a. The strands of this series, before moving to 
the margins of the antero-posterior flanks of the leaf-trace, link up together 
irregularly and separate again before leaving this odd strand in the middle of the 
adaxial face of the petiole. This median strand at first possesses both xylem and 
phloem. The xylem dies out first, as the strand, without moving to right or left, 
runs up the petiole ; then the phloem also disappears into the ground tissue. 
Meanwhile, as the leaf-trace approaches the level of the first pinna, the strands 
on one margin of its antero-posterior flanks (consisting in part of half of the series 
of strands originally occupying the adaxial face of the petiole) divide off several 
small strands, of which four at the extreme tip move out towards the pinna 
(text-fig. 9c, d). Then from the opposite flank a similar group moves from the 
margin into the second pinna (text-fig. 9 d, e). Above the lowest pinnae the 
leaf-trace is widely open on the adaxial face and narrowed on the abaxial curve 
(text-fig. 9 f), the succeeding pinnae being supplied, like the earliest, from the 
adaxial margins of the series of leaf-trace strands. 
d e 
Text-fig. 9. 
