io8 Ford . — The Anatomy of 
are derived from these as branches, being of secondary 
development. 
Jeffrey 1 has described in detail the development of the 
steles in the rhizome of Pteris aquilina , and has found that 
the large central strands are not primitive as is generally 
thought, for they are given off as small branches from the 
true primitive axial steles which can be traced into the rhizome 
from the primary root. These large, secondary, axial strands 
are therefore regarded by this author as medullary bundles. 
It seems possible to compare these secondary axial strands 
of Pteris aquilina with those found in Ceratopteris . In both 
cases they are given off from the primary steles and come 
to lie in the centre of the stem. In Pteris , however, they 
increase considerably in size until they are equal to, or larger 
than the steles from which they have been derived, whilst in 
Ceratopteris , on the other hand, they decrease and finally die 
away. 
5. The Apex of the Stem . The apex of the stem of 
Ceratopteris is surrounded by the young leaves, which enclose 
it on all sides, completely hiding it from view. Large numbers 
of ramenta are also present, and these cover the immature and 
developing leaves as well as the apex itself. These ramenta 
are but one cell thick ; when seen in surface view the in- 
dividual cells have a sinuous outline. 
The structure of the apical region of the stem is best 
studied in a median longitudinal section taken through the 
apex. Transverse sections through the same region also show 
interesting points. Fig. 9 is reproduced from a photograph 
of a median longitudinal section. In the centre lies the actual 
apex of the stem itself, in the form of a curious cone-shaped 
prominence, at the summit of which the three-sided apical cell 
is found. The cells composing this apical cone are large 
and have conspicuous nuclei which stain deeply. On each 
side of the cone the young leaves are found, arching over 
towards the apical cone which stands erect. This cone- 
shaped apex reminds one very strongly of that found in 
1 Jeffrey, 1899, p. 605. 
