THE LEAF-TRACE IN SOME PINNATE LEAVES. 
17 
Cycas revoluta, Thunb. 
In the other genera of the Cycads the leaf-trace has a more complex form. The 
outline of that of Cycas revoluta , Thunb., is well known. In text-fig. 10a the 
leaf-trace below the first pinna is shown. The abaxial curve, which is prominent, 
is linked to the adaxial arcs by a double row of strands on the antero-posterior line. 
The abaxial curve runs up almost unchanged until near the tip of the rachis, though 
it shrinks gradually (text'-fig. 106), and is markedly reduced below the terminal 
pinnae (text-fig. 10c). The strands of the abaxial curve fuse among themselves 
5 
Text-fig. 10. 
and with the strands connecting the curve with the adaxial arcs, while the adaxial 
arcs are reduced in size as they ascend the rachis. The pinna-traces are derived 
wholly from the outwardly-turned margins of the adaxial arcs, the marginal strands 
of which pass directly into the pinnae. This is the process below the basal pinnae, 
as well as below the terminal pair. As the marginal strands pass out into the 
pinnae, neighbouring strands take their place, and the strands of the antero-posterior 
line and those of the abaxial curve are gradually moved towards the adaxial face of 
the petiole, to replace the departing strands of the adaxial arcs, until below the 
ultimate pinnae the leaf-trace is reduced to three strands only (text-fig. 10c). 
Zamia Lindeni, Regel. 
A similar process takes place in the leaf of Zamia Lindeni, Regel, the pinna- 
traces being given off from the margins of the adaxial portion of the leaf-trace 
(text-fig. 11a, 6), while the abaxial curve is employed again to make good the 
drain on the adaxial strands. The leaf- traces of Ceratozamia Kuesteriana, Regel, 
and Macrozamia Denisonii, F. Muell., are similar in outline to that of Zamia 
Lindeni, and supply their pinnae in the same fashion. 
TRANS. ROY. .SOC. EDIN., VOL.' LII, PART I (NO. 1). 
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