Stem of Angiopteris evecta. 515 
the centre may possess only isolated groups of spiral tracheides, 
while a third, nearest of all to the axis of the stem, shows only 
an arc of protophloem. The method of development of the stele 
can thus be followed in a single transverse section of the stem. 
The concentric structure of the steles with the protoxylem 
arranged as just described is found in the steles occurring in 
the leaf-bases, the normal structure of the leaf-bundles only 
making its appearance where the swollen leaf-base passes 
over into the petiole proper. 
As has been frequently stated by previous investigators, no 
endodermis is present round the stem steles. 
The smallest elements of the protoxylem are spiral 
tracheides, but somewhat larger tracheides have a form of 
thickening transitional between spiral and scalariform, which 
may be described as reticulate. The spiral and reticulate 
tracheides occur both at the periphery and in the centre of 
the stele, and are seen in longitudinal section in Fig. 31. 
The large sieve-tubes with their transverse walls are similar 
in structure to those described by Poirault 1 for the petiole 
and root. 
As is well known, the stem of Angiopteris is destitute of 
sclerenchyma, though this is present in the petiole. 
Investigations into the character of the actual apex of the 
stem have not been successful in obtaining any definite result 
The stem apparently ends in a flattened or a very slightly con¬ 
vex surface, which is protected by the young leaves with their 
stipules. In the centre between the youngest leaves the apical 
tissues are visible as a small white spot, due to the large size 
of the cells in this region. The actual apex is occupied by 
several large cells, but the exact arrangement of these could 
not be determined owing to failure to obtain an accurately 
transverse section. These cells may be the product of division 
of an apical cell, or there may be several initial cells as is 
certainly the case in the apices of the leaves. The vascular 
strands can be traced up very near the position of these 
apical cells in the form of strands of small-celled meristem. 
1 Poirault (’94), pp. 139 , 194 . 
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