Danaea and other Marattiaceae . 533 
comes merged in, this curved plate of tissue (for such it is 
in reality), only to be again given off higher up. The next 
commissural branch may, however, be given off before the 
previous one is merged in the curved plate, Fig. 29, diagram 
XII, K.o-., central strand, c.s., new commissural branch. In the 
next diagram <7. is the upward continuation of K.o-., and at 
a slightly higher level it will anastomose with the meristeles 
on each side of it and the incoming root, R. In these two 
diagrams the small meristele, is one of a leaf-trace pair, 
the other will be given off from the long meristele opposite 
at the end marked I t. The next diagram, XIV, shows the 
formation of a trimeristelic leaf trace referred to above. The 
small strand, /./., became free at a considerably lower level, 
and the two remaining strands of the trace will be given off 
from the large meristeles marked l.t. at their outer ends. 
This trimeristelic leaf-trace was formed twice, before the 
tetrameristelic condition was attained in this seedling. Dia- 
grams XV-XIX show a further modification in the behaviour 
of the central strand, and the formation of a tetrameristelic 
leaf-trace. In this case the central strand, after it reaches its 
peripheral position in the centre of the leaf-gap, gives rise to 
two branches, c.s. and c!s! These branches unite at a higher 
level, and the central strand is restored (diagrams XVIII, XIX). 
This state of matters was found in two different seedlings. 
Diagrams XV to XIX are not consecutive sections, but are in 
sequence, and show a typical and frequently recurring state of 
matters. Diagram XV illustrates the nearest approach to in- 
ternodal structure met with, and already referred to. Diagram 
XVI shows the maximum number of meristeles present at 
this phase, a-f. The strands a , b , c, d , will become leaf-trace 
meristeles. They, however, do not leave the dictyostele 
without first anastomozing and again separating before passing 
outwards as the leaf-trace meristeles, as seen in the succeeding 
diagrams. In Diagram XIX the four leaf-trace meristeles 
have now definitely left the dictyostele, and the two branches 
of the central strand have completed their fusion. The 
meristeles, e. and /., together with branches from a will give 
O o 2 
