778 
Notes. 
consists of a central mass of small scalariform tracheids, without any 
conjunctive parenchyma. The phloem consists of a layer of small 
sieve-tubes separated from the xylem by a layer of parenchyma. The 
pericycle may be absent or only imperfectly represented. There is 
a definite endodermis, but the constituent cells are not clearly always 
the innermost ones of the extrastelar parenchyma. 
When the cotyledon-trace is about to be given off, the xylem of this 
vascular axis, or ‘ protostele/ is separated into more or less unequal 
portions by a layer of parenchyma. The parenchyma increases in 
amount, and ultimately the cotyledon-trace is separated from the 
central stele. The cotyledon-trace is collateral. The next few leaf- 
traces are given off in the same manner, and are likewise collateral. 
The stele resumes its simple ‘ protostelic ’ appearance. Cauline roots 
occur, but not regularly. 
As further leaf-traces depart from, and root-traces join the vascular 
axis, the primitive structure is gradually modified, and it may become 
more or less crescentic, forming an incomplete, or even complete, 
gamostelic ring. The spaces left by the departure of the leaf-traces 
now constitute leaf-gaps. The vascular tissue of this stage may be 
described as a ‘ siphonostele with leaf-gaps.’ 
The time of appearance of the first mucilage-canal varies. The 
earliest occurrence noted was after the third leaf-trace had been 
differentiated. 
In one seedling a curious ligament of phloem was observed, which 
pursued an oblique course upwards and connected the two horns of 
a crescentic vascular mass. This strand of phloem interrupted the 
course of the central mucilage-canal. 
At first the leaf-traces are simple and collateral ; later they are 
simple and concentric; still later each trace divides into a pair of 
strands as it recedes from the axis. At a higher level the leaf-trace 
consists of a pair of strands, each of which takes its departure 
separately. 
A remarkable deviation in the early stages of development was 
shown by one seedling. A mass of parenchyma early made its 
appearance in the centre of the xylem, simulating a pith. Careful 
examination showed that this was due to abortion of the cotyledon 
and its trace, and exceptionally early preparation for the departure of 
the three succeeding leaf-traces. 
2. Stele of the Marattiaceae. 
