ANATOMY OF CERTAIN SPECIES OF ENCEPHALARTOS. 449 



entirely devoid of mucilage-canals. At the end of the dry season adventitious roots are 

 emitted by the stem, fresh leaves are put forth, and growth proceeds as before. 



A transverse section through the upper and thickest portion of one of the adventitious 

 roots, close to its junction with the stem, exhibits a very thick cylinder of xylem enclosing 

 a fairly wide pith ; the phloem is very much narrower than the xylem and the inner 

 contour of the xylem is almost circular, and I could not discern how many protoxyhim- 

 groups were present. Great numbers of sclerotic cells occur in all the parenchymatous 

 tissues and in the phloem. Mucilage-cells are absent. 



The most interesting feature of the root is the presence, immediately outside the large 

 cylinder, of one or two smaller cylinders or concentric strands, w4iich are possibly not 

 entirely closed on their inner side. Their elements are extremely irregular in position and 

 course, many of the segments composing them running tangentially instead of vertically. 

 Each encloses a pith containing great numbers of sclerotic cells. They are probaldy entirely 

 secondary in origin, and are doubtless homologous with the similar strands occurring in 

 the roots of Cycas revoluta *, Thunb. They fuse with the main cylinder lower down, 

 ;and thus occur only in the upper and oldest part of the root where it adjoins the stem. 



In one thick root examined the jnth of the large cylinder is full of tracheides, contorted 

 and involuted in every conceivable direction. They appear to be merely tracheides of 

 the imier part of the xylem, which lias, for some strange reason, assumed this unwonted 

 and anomalous course in the pith. 



Younger roots are triarch and diarch in structure. 



E^fCEPHALARTOS HORRIDTJS, Lehm. 



I examined a plant of this species from the Palm-house at Kew, having an axis 4-6 

 inches in thickness. 



The central cylinder of the stem gradually narrows in diameter as it passes down into 

 the ta/p-root, w^hich in this specimen is preserved. Considerable irregularity prevails in 

 the setting and position of the tissues in the lower region of the stem. On one side of 

 the cylinder, in the transitional region betw^een stem and root, and immediately on its 

 outer periphery, as seen in transverse section, occurs a large vascular strand with a 

 great amount of xylem and phloem, all probably of secondary origin (fig. 9, cs^). This 

 strand evinces a tendency towards a coticentric structure. It is perfectly similar to and 

 homologous with the semi-concentric strands situated on the periphery of the central 

 cylinder, which some time ago I noted in the transitional region between root and 

 stem of a small plant of Macrozamia Demsonii, F. Muell., as also with the similar 

 strands in the same region in Cycas reroluta, Thunb. Like those in the latter plants, the 

 strand under consideration has connections with the central cylinder. On the dorsal 

 side of, and closely abutting on, this large strand occur at one level two other smaller 

 ones of the ordinary collateral structure and orientation (cs-). At another level two 

 strands are seen, one on each side of the large one, each with a considerable amount of 



* WorsdeU, " The Comparative Anatomy of certain Genera of the Cycadaceae," Journ. linn. Soc., Bot. vol. xxxiii. 

 1898, p. 440, pi. 20. fig. 5. 



