io Lcin%.—Shi dies in the Morphology and 
adaxial extension of xylem was incomplete at division, is given in PL I, 
Photos 7-9. In such cases no definite clepsydroid stage is passed 
through. 
Even in the large mesarch traces described above, the inner xylem was 
found to diminish in the region of the nascent leaf-trace (cf. PL II, Photo 21). 
As a rule, in smaller rhizomes, where the centripetal xylem is less strongly 
developed, the inner xylem completely disappears from the middle of the 
concavity of the nascent trace, so that the parenchymatous tissue is con¬ 
tinuous from the pith to the protoxylem. The trace thus separates from 
the stele with xylem, which is either completely endarch or has only traces 
of inner xylem to the two sides. Thus there is very little inner xylem in 
the trace figured in PL I, Photos 7-9, while Photo 10 shows a purely endarch 
trace which had just departed from another rhizome. This latter trace 
divided without any indication of adaxial completion of xylem. On the 
other hand, the trace shown in PI. Ill, Photos 47-49 was endarch at its 
departure, but almost at once showed adaxial completion of its xylem. 
The last-mentioned specimen thus illustrates another variant in which 
the adaxial completion of the outer xylem of the trace takes place while 
the latter is still monarch (Photo 48). This was followed later by the 
assumption of the clepsydroid structure preceding the division of the trace 
(Photo 49), which took place in the outer region of the cortex. 
This pre-clepsydroid condition, in which the trace is adaxially com¬ 
pleted, but has an undivided protoxylem, may be maintained until the trace 
has left the cortex of the rhizome. This was the case throughout a large 
fragment of rhizome which bore a branch, to be described later, and the 
progress outwards of one trace can be followed in Text-fig. 6 from the right 
side of the rhizome. This trace as it left the cortex is also shown in PL I, 
Photo 11, while Photos 12 and 13 on the same plate show another trace 
from the same rhizome, just before the xylem was completed adaxially and 
after this had been effected. There is no room for doubt as to the adaxial 
completion of the xylem in these traces, and the reality of the process is 
confirmed by the accompanying completion of the phloem, which is seen 
in Photo 13; and this is even better shown by the next rhizome to be 
described. 
This piece of rhizome will be referred to later in the paper as showing 
a rapid progression from the juvenile to the adult type of structure. The 
type of leaf-trace departure, which was maintained at each node, was 
remarkable in that the xylem of the trace was completed adaxially before 
or as it separated from that of the stele. As the xylem of the trace 
enclosed little parenchyma, it was possible on the one hand that its adaxial 
portion represented the very early completion of the outer xylem of the 
trace, or, alternatively, that it was the continuation outwards of the inner 
xylem of the mesarch stele. Direct observation supports the former 
