248 
Davie . — The Structure and 
Internal Structure. 
The stock is distinctly an upright one, widening gradually from the 
base upwards. It is covered by paleae of delicate texture and dark 
brown colour. Some of these are provided with numerous glands on 
the surface directed towards the stock. The whole stock is enveloped 
in a thick mass of sclerenchyma, several cell-layers in width. The ground 
parenchyma is compact, with few air spaces and those of small size, 
while the cells are filled with starchy and proteid contents. Throughout 
this parenchyma are scattered little masses of sclerenchyma, dispersed 
in irregular fashion, but of very firm texture. The leaves are inserted 
spirally on the stock, the divergence in the mature stock being one-seventh. 
A transverse section of the stock shows a series of meristeles, usually five or 
six in number, surrounded at their edges by a varying number of smaller 
strands (Fig. 2). One or two of the meristeles are elongated, and in trans- 
verse section show tracheides cut in an oblique or in a longitudinal direction. 
Other meristeles are rounded and have quite transversely-cut tracheides. 
If one of the elongated meristeles is followed up or down in the stock it is 
found to divide into two parts which assume a structure exactly like that of 
the remaining meristeles. Sometimes two elongated meristeles may be 
found opposite to each other. Generally, however, only one oval meristele 
appears in each section. This shows at once that the vascular system 
is dictyostelic. On dissection of the stock this dictyostele is found to con- 
sist of a series of strands united into a meshwork, in which the gaps have 
an oval form. It is indeed exactly like the advanced dictyostele generally 
exemplified in the vascular system of Nephrodium filix-mas , Rich. The 
gaps are found only opposite the entrance-points of leaf-traces into the 
dictyostele ; there are no perforations. 
The leaf-trace is itself made up of three main strands and four or five 
subsidiary ones. Two of the main strands occupy the adaxial corners 
of the petiole, while the third occupies a median position on the abaxial 
curved side. Two smaller strands are found between each adaxial main 
strand and the median one, while often still smaller strands, of the nature of 
commissures, may be found between these subsidiary strands or between 
them and the main strands (Fig. 3). Sometimes a commissural strand 
may be nipped off from one of the adaxial strands, pass up to the next 
subsidiary strand, fuse with it on one side, then pass off on the other side, 
to unite with the next subsidiary strand a little further up the petiole. 
This process is continued up the petiole, the commissural strand passing 
from one strand to the next until it arrives at the second adaxial strand of 
the petiole. 
When the leaf-trace strands are followed from the petiole into the 
dictyostele they are found to insert themselves along the sides of the oval 
