768 cle Bntyn .— The Ontogenetic Development of the 
in which the centre of the petiole is often for part of its course sclerotic. In 
Gleichenia dicarpa , belonging to the sub-genus Englcichenia , the central 
region, which Boodle 1 regards as being pericycle, consists partly of paren¬ 
chyma, partly of sclerotic elements. No internal endodermis is present here, 
but it is found in other species of Gleichenia. The petiole of the sub-genus 
Mertensia has an invaginated endodermis. Boodle writes of it (p. 716): ‘ The 
central region is occupied by sclerotic tissue continuous with the cortex and 
apparently belonging to it instead of to the pericycle as in G. dicarpal In 
G. pedalis the endodermis is only slightly incurved, and here the pericycle 
is again partly sclerotic as in some Eugleichenias. We see, therefore, that 
in Gleichenia there seems likewise to be a tendency to form sclerenchyma 
in the central part of the stele, and this is brought about in the different 
species in various ways resembling the different structures of D. conjugata. 
Often tannin sacs are not present at the base of the petiole, but appear 
at a higher level; this is also the case with the protoxylems. Division of the 
stele into two by constriction in the median vertical plain takes place only 
just before the lamina is reached and is soon followed by a second division. 
The veins of the leaf are collateral. 
Dipteris Lobbiana. 
Stem. Dipteris Lobbiana has in many respects the same characters as 
D. conjugata. Fortunately the very first stages were present, but the series 
were more incomplete and broken than those of D. conjugata. 
The diarch primary root passes into a protostele (Fig. 4, PL LVII). A 
part of the xylem projects and passes out as the first leaf-trace. The further 
stages often show the same types as are found in D. conjugata. The Lindsay a 
stage is passed through and a few dark cells are formed in the centre, and 
these disappear again afterwards. A xylem-ring is formed with unequally 
developed ventral and dorsal side, but the difference in thickness of the two 
sides is not so striking as in D. conjugata. 
In one of the series we find the stage represented by Fig. 15, PI. LVIII. 
The xylem has the appearance of not being fully differentiated yet, and 
the section looks as if it were near the meristematic region. Some sections 
nearer the stem apex, however, the xylem-elements increase very much, in 
connexion with the formation of a root (Fig. 16), and some sections 
further on still a complete xylem-ring is formed again. This ring is only 
one cell thick at the dorsal side and the xylem is much more developed at 
the point of insertion of the root. This series is again an example of the very 
irregular development which is so striking a character in D. conjugata. The 
increase of xylem-elements in connexion with root-formation is a very 
constant feature. When the meristematic region is reached, the xylem is 
1 Boodle: On the Anatomy of the Gleicheniaceae. Ann. of Bot., vol. xv, 1901, p. 714. 
