342 THE JOURNAL OF BOTANY 



stand. The bundles show the usual monocotyledonous structure: 

 one or two protoxylem elements ; two metaxylem vessels ; and a 

 patch of phloem, consisting of sieve tubes and companion cells. 

 The bundles are united into a cylinder by sclerenchyma, and the 

 skeletal tissue is surrounded by an endodermis with well-marked 

 thickenings on the radial walls (fig. 4). A longitudinal section of 

 the stem shows that both the proto- and metaxylem elements 

 have annular thickenings, the first-formed elements being recog- 

 nisable by the wide spacing of the rings (fig. 6). The walls of 

 the sclerotic cells also are covered with very fine pits, which are 

 absent from the sclerotic cells developed in other places ; this 

 seems to suggest that they form accessory water-conducting 

 elements. 



Structure and development of the leaf. — Each leaf is closely 

 adherent to the stem through one internode. It then becomes 

 free, but remains tubular for about half or two-thirds of its 

 remaining length. There are on an average eight or nine bundles 

 in each leaf, each bundle consisting of a small group of xylem 

 cells (3-8) and a somewhat larger group of phloem cells, with a 

 large patch of sclerenchyma towards the outside ; smaller inter- 

 fascicular patches of sclerenchyma also occur. The outer surface 

 of the leaf in the young condition shows an epidermis with 

 curiously irregular walls — probably due to incomplete thickening ; 

 the cells are of two sizes, long and narrow cells alternating with 

 very short ones (fig. 8). The latter give rise to the backwardly- 

 directed hairs to be found in the older leaves. As one would 

 expect in an underground stem, there are no stomata and no 

 palisade tissue, the ground tissue of the leaf being made up of 

 loose parenchyma without chlorophyll. 



Origin of leaf. — A longitudinal section passing through the apex 

 shows leaves in all stages of development. An incomplete arc of 

 merismatic tissues appears just below the actual apex; this grows 

 rapidly, forming a sheath which is not quite complete. Later, 

 the merismatic arc at the base of the sheath becomes a complete 

 ring, and the remainder of the leaf is tubular. A longitudinal sec- 

 tion, such as that figured (fig. 5), shows the two innermost leaves, 

 consisting entirely of rapidly-dividing cells ; the third leaf bears 

 signs of differentiation, its cells are usually elongated, particularly 

 those towards the outside where the sclerenchyma and vascular 

 tissue will be laid down. The internode also shows a strand of 

 delicate elongated tissue leading up into, and continuous with, 

 the elongated cells of the leaf, forming the procambium of the 

 vascular cord. The internode below the fourth leaf shows a 

 xylem strand which is continuous with one in the leaf itself, and 

 a more fully developed strand nearer to the centre of the stem. 

 The fifth leaf shows all the characters of a completely developed 

 organ. In many cases buds are developed in the axils of leaves ; 

 and there is usually a great development of tracheal tissue 

 immediately below, connected to the bud by strands of elongated 

 cells (fig. 5). 



Origin of roots. — The roots arise endogenously from the under 



