Danaea and other Marattiaceae. 
535 
not always, comes in medianly, and there is frequently one 
root for each leaf. Its fusion 1 with the dictyostele is usually 
associated with the closing of a leaf-gap, and synchronizes 
with the junction of the central commissure with the dictyo- 
stele 2 . The meristeles, whether of the dictyostele, the out- 
going leaf-traces, or the fronds, are all built very much upon 
the same plan, viz. the usual Marattiaceous type. The phloem 
of the seedlings is so narrow in the radial direction, that it is 
practically impossible to distinguish proto- from a later formed 
phloem, as can be done in the case of older and adult plants. 
The protoxylem in the leaf and leaf-trace meristeles is endarch, 
as usual for the family, and more or less clearly mesarch in the 
dictyomeristeles. There is very little sign of what Farmer 
and Hill call secondary thickening , or of secondary merismatic 
division of the ground-parenchyma, except as a result of 
injury or undue pressure. The Marattiaceae generally have 
a great tendency to form what seems to be wound-periderm, 
but more will be said of this when dealing with the compara- 
tive anatomy. A small peculiarity that might be noticed en 
passant is the occurrence of an isolated tracheid in the 
ground-tissue in a leaf-base. It is of no great importance 
except in helping to show that the line to be drawn between 
stelar and extrastelar tissue is not a hard and fast one. This 
question will be dealt with under the heading ‘ Review of 
Terminology in Relation to Morphology.’ 
The study of the transverse sections of the seedlings of 
Danaea simplicifolia inevitably leads to a belief in the impor- 
tance of the central strand or ‘sympodial commissural 
column.’ It is undoubtedly the one part of the dictyostele 
which is purely cauline. If the parts of it, where it is con- 
tinuous with the other meristeles, be included, it may be said 
to follow a somewhat zigzag spiral course, because its points 
of junction move through the same angle which is described 
1 It has constantly to be borne in mind that this is only a descriptive fa$on de parley. 
2 If one were to imagine a transverse section across Fig. 4 (Farmer and Hill, 
loc. cit.) at the level of the lettering rt. 3, one would have a very good idea of the 
state of matters in D . simplicifolia as described, but generally the root is more 
median, and opposite the commissure. 
