534 Brebner . — On the Aitatomy of 
rise to the next leaf-trace, which also consists of four meri- 
steles. The meristeles, e. f, in their turn, behave as a. b. did 
at the lower level. After this stage is reached there is little 
further complexity attained as far as the oldest seedlings 
available showed. Judging from the adult rhizome of D. alata , 
such changes as do occur are due to an increase in the number 
of the leaf-trace meristeles and the tendency of the meristeles 
generally to branch and anastomose, as is so strikingly illus- 
trated in the case of Angiopteris. 
In this way, then, the somewhat irregular or adelosiphonic 
dictyostele of Danaea is established, viz. by a process which 
is, to all intents and purposes, a branching of a haplostele, 
due to the departure of the leaf-traces of closely set, spirally 
arranged leaves. The complications which arise are due to 
a tendency of the meristeles themselves to branch, to the 
formation of a central commissural column, and to the pre- 
sence of an abundance of cauline roots. 
It will be appropriate to note here a few remaining points 
of interest in the anatomy of these seedlings. It was 
mentioned that the central strand sometimes begins as 
a phloem-commissure only. It is therefore not surprising 
to find meristeles losing their xylem and continuing their 
course as phloem-strands, till they rejoin the system at a 
higher level. Farmer and Hill found that the central com- 
missures sometimes ended blindly in their upward course. 
That was not observed in Danaea , but the time and manner 
of its branching varies a good deal. For instance in the 
seedling from which Figs. 28 and 29 were drawn, at a stage 
subsequent to that of the double branch shown in Diagrams 
XV-XVII, first one branch was given off, and then another 
followed, the latter anastomozing with the former on the way 
upwards and across. In the oldest seedling cut, not more 
than two commissural branches were given off at any level, 
and the later ones only differ from those figured in their 
greater size and importance. 
The root (R. in Figs. 28 and 29) behaves in a fairly constant 
manner. When the leaf-trace is paired, it generally, though 
