450 BOTANICAL GAZETTE [JUNE 
leads to the formation of an outwardly projecting tooth (fig. 1, 
stage 4). The tracheids at the outer edge of the tooth are very 
small, and have exactly the same appearance as those at the outer 
edge of the parallel bands of metaxylem (st of the figures). Their 
thickening appears to be a fine reticulum. The more internal 
elements of the metaxylem, both those of the crossbar, which 
becomes radially deeper, and those at the thickened bases of the 
former internodal lateral bands, assume more and more the appear- 
ance of typical nodal tracheids of Equisetum; some of them are 
already much widened radially. The bundles increase in width, 
but are still separated by intervals wider than themselves. The 
carinal canals are still large, but become narrower radially. The 
median tooth of metaxylem eventually projects nearly as far as 
the ends of the lateral bands and the concavities between it, and 
then becomes much shallower, owing to the great increase in 
number of nodal tracheids. This is the phase shown in fig. 1, 
stage 5. The small concavities in the xylem on each side of the 
median tooth seem to be occupied chiefly by metaxphloem. 
Soon after this stage has been reached, the smaller outer 
tracheids of the median tooth begin to project more and more, and 
the tooth becomes less acute in outline. At the same time two to 
four rows of tracheids, lying internally to these small projecting 
tracheids, are replaced by parenchymatous cells. In this way 
the inner part of the bundle is divided by a narrow parenchymatous 
gully, continuous with the two or three layers of parenchyma that 
separate the carinal canal from the nodal tracheids. ‘The carinal 
canal is now markedly narrower radially, and usually contains at 
its outer edge, opposite the parenchymatous gully, the remains of 
two or three partially disorganized tracheids. This condition is 
represented diagrammatically in fig. 1, stage 6. Almost immedi- 
ately after the formation of the parenchymatous gully a few of the 
partially disorganized tracheids of the protoxylem may be seen to 
bend outward from the carinal canal, which here bulges a little 
outward. These tracheids now, no longer disorganized, run through 
the parenchymatous gully and fuse with the small oval mass of 
tracheids that forms the upward continuation of the small tracheids 
at the apex of the median tooth of metaxylem. These latter 
