Danaea and other Marattiaceae . 527 
for the almost simultaneous departure of the next three 
leaf-traces. At a higher level the whole thing has resolved 
itself into a state of matters such as shown in Fig. 5, with 
the difference that there are three outgoing leaf-traces in- 
stead of two. The remaining leaf-traces w T ere given off in 
the usual way, and there was only one cauline root. This 
seedling is mentioned on account of its apparent pith, but 
it is so abnormal that much importance cannot be attached 
to it. It is interesting to note that sieve-tubes, &c. appear 
in the central parenchyma. As already mentioned, the earlier 
leaf-trace meristeles are collateral, but those developed later 
are concentric, hence according to Van Tieghem’s terminology, 
the former would not be 4 steles ’ and the latter would. With 
regard to the leaf-traces themselves, the earlier ones are mono- 
meristelic 1 and collateral ; later they become concentric. 
The next step is that the xylem becomes separated into 
two masses as the leaf-trace passes out, but without actual 
dichotomy. Later, i. e. at a higher level, the originally single 
meristeles dichotomize, and finally they are given off sepa- 
rately ab initio. To take a concrete example:' — One of the 
seedlings microtomed had thirteen leaves and therefore leaf- 
traces. The first six outgoing leaf-traces were monomeristelic 
and monoxylic, the seventh was at first monoxylic and became 
dixylic. The eighth was monomeristelic and then became 
dimeristelic through dichotomy. The ninth behaved much as 
the eighth, the tenth was dimeristelic from the start. The 
meristeles of the tenth leaf-trace, when they reached the leaf- 
base, each gave off a strand to the stipules, which were now 
distinctly developed. The eleventh, twelfth and thirteenth 
leaf-traces behaved as the tenth. 
The following is a short account of the general sequence of 
events in the formation of the dictyostele from the haplo- 
stele. First of all, there is the haplosteie with a solid core of 
tracheids, this becomes somewhat oval in outline, a layer 
of parenchyma divides the xylem into two more or less 
equal halves ; this parenchyma increases in amount till it 
1 See Introduction, p. 522. 
