4 Miss Robertson, Notes on the Anatomy of 



the stem these bundles form a fairly complete ring, but it is never 

 very regular, and at the level where the diameter of the inner ring 

 is about 7 cms., the outer ring though well-marked on one side 

 of the stem is only slightly developed on the other. 



At the base of the stem the number of concentric rings of 

 vascular tissue increases, and the different zones are seen in longi- 

 tudinal section to anastomose together (Fig. 6). There appear, 

 at the extreme base, to be as many as four extra rings, but the 

 whole structure is irregular and difficult to make out. As Con- 

 stantin and Morot 1 have pointed out for Gycas Siamensis, En- 

 cephalartos Alteinsteinii and Ceratozamia Mexicana, the existence 

 of the supernumerary bundle-systems and their early appearance 

 at the base of the stem, are connected, as in the case of secondarily 

 thickened monocotyledons, with the need of obtaining an adequate 

 vascular supply for the adventitious roots which are destined to 

 make up for the insufficient development of the tap root. 



I have not been able to find any tertiary inverted strands 

 between the vascular rings, such as those described by Worsdell 

 in Macrozamia Fraseri. 



(iv) The Gorteoo and Leaf-traces. 



Transverse sections through the cortex near the apex shew 

 numerous leaf-traces cut transversely, as in this region they run 

 nearly vertically to join the central cylinder lower down. Above 

 the level of differentiation of the central cylinder, I noticed a single 

 horse-shoe-shaped bundle in the cortex among the normal leaf- 

 traces. This was the nearest approach I have seen in any part 

 of the stem to a concentric bundle. In radial sections somewhat 

 lower down, but still in the younger part of the stem, the leaf- 

 traces can be followed running obliquely upwards from the central 

 cylinder, right to the bases of the leaves. It seems that the 

 characteristic Cycadean girdles, of which traces can be seen in 

 transverse sections in the form of short horizontal strands of 

 spiral tracheids, run so close to the leaf bases as to be cut off 

 by periderm at a very early stage. In the older part of the stem 

 the horizontal radially-running portions of the traces dip down 

 as they approach the central cylinder, and passing through the 

 outer ring join the inner ring. In one case a trace was observed 

 to fork in the cortex, and the two branches united a little further 

 out, forming a loop. Occasionally when a trace is followed out- 

 wards from the central cylinder it can be seen to turn when it 

 gets near the periphery and take a course parallel to the surface 



1 "Comparative Anatomy of certain species of Encephalartos," Trans. Linn. 

 Soc. Vol. v. Part xiv. 1900, p. 447. 



