370 Boodle . — Anatomy of the Schizaeaceae. 
Lygodium, root. 
The root of L. dichotomum has a diarch xylem-plate with 
sometimes two specially large tracheides in the metaxylem, 
as occurs in many other Ferns. The tracheides at each end 
of the xylem plate, including the protoxylem and a few other 
tracheides, are somewhat spread out as a tangential row of 
elements at right angles to the plane of the diarch plate. The 
two protoxylem-groups consist of a few small tracheides, and 
are in the usual position. After their differentiation the sub- 
sequent order of development of the xylem is tangentially 
outwards for the one or two larger tracheides completing 
the tangential rows mentioned above, and at the same time 
inwards (towards the centre of the root) for the remainder 
of the metaxylem. The development here and comparison 
with the structure in other species do not appear to give any 
grounds for distinguishing by a separate term the tangentially 
developed tracheides from the more central part of the xylem. 
Hence ‘ metaxylem ’ may be used for all the xylem other than 
protoxylem, as in the previous paper (Boodle, ’00, p. 458). 
The endodermis consists in most cases of six flattish cells, 
whose radial walls correspond roughly with those of the 
cortical layer next outside ; this layer also consists of six 
cells, which measure tangentially two to three times their 
radial depth, and have brown walls. Outside these cells 
there is a sudden change to many-celled layers, of which the 
next 1-3 layers are thick walled (according to the age 
of the root). The innermost of these may consist of very 
thick- walled cells with narrow radially elongated cavities. The 
remaining five or six layers of the cortex have comparatively 
thin brown walls. The pericycle is one cell thick in most 
places, and is a many-celled layer, but appears to have been 
formed by subdivision of a six-celled layer, whose radial walls 
at first corresponded with those of the endodermal cells. 
The root of L. pinnatifidum is fairly like that of the species 
just described, but the endodermis consists of twelve or more 
cells. When the root-stele passes off from the stele of the 
