8 
Lang . —Studies in the Morphology and 
middle line, but otherwise continues the series of changes shown in Text- 
fig. 2. In Text-fig. 3, A, the endodermis is seen interrupted on the side 
away from the middle line, though on the other side it is continuous from 
the leaf-trace to the stele. The external and internal endodermal layers 
have become continuous round the margin of the leaf-gap. The leaf-trace 
is distinctly mesarch and the protoxylem elements form an interrupted 
band between the two xylems. In Text-fig. 3, B, the trace is completely 
separate, and comparison with the earlier stage will show that the arc of 
xylem is becoming more curved and is tending to complete the tube of 
outer xylem on the adaxial side. The persistence of the centripetal xylem 
internal to the protoxylem enables a clear distinction to be drawn between 
true mesarchy of the trace and this adaxial completion of the xylem. The 
Text-fig. 3. Series of sections from the same rhizome as Text-fig. 2, to show the later stages 
in departure of a leaf-trace, the adaxial completion of the xylem, and the clepsydroid stage passed 
through before division. Further description in text, e ., endodermis of leaf-trace ; ph ., phloem ; 
x.o. y outer xylem ; px ., protoxylem of leaf-trace; x.i. } inner xylem; p.r ., pith of base of root. 
trace in Text-fig. 3, B, shows preparations for division in that the protoxylem 
is present as two laterally placed groups; a projection of metaxylem 
between these is also to be noted. In the next stage figured (Text-fig. 3, c) 
the outer xylem has become complete adaxially and so has the endodermis ; 
the phloem was not completed in this trace. The projection of xylem 
noted in the preceding stage has become continuous with the adaxial 
xylem, and divides the parenchyma in the concavity of the xylem into two 
areas. In each of these, internal to the protoxylem, centripetal xylem still 
occurs, though it is more poorly represented than lower down. Shortly 
after this, when the trace is approaching the outer part of the cortex, it 
divides into two. A stage of the division is represented in Text-fig. 3, D, 
and it will be noted that in this case the outer xylem forms a complete ring 
in one half of the trace and not in the other. The inner xylem is still 
