7 o6 Boodle . — Anatomy of the Gleicheniaceae . 
chyma, and surrounded by a continuous ring of phloem, 
pericycle and endodermis. There is thus a general resemblance 
to the structure of the rhizome of Lygodium , but a point 
of difference is that in Gteichenia the xylem is mesarch, and 
has several distinct groups of spiral protoxylem-elements. 
The only other widely different type of structure found in 
the genus is the solenostelic, which has so far been observed 
only in G. pectinata. It will be convenient to describe the 
species, which possess a protostele, first, and to treat G. 
pectinata separately. 
In each species the diameter of the rhizome is of course 
liable to variation according to the vigour of the specimen, 
but two examples will give an idea of the sizes met with. A 
rhizome of G. polypodioides measured about i mm. in diameter, 
while one of G . pubescens reached rather more than 3 mm. 
These, as compared with other species, may be taken as a small 
and a large rhizome respectively. The proportionate dimen- 
sions of stele and cortex in G. flabellata are shown in Fig. 1, 
Plate XXXVIII. In this diagram a . represents the epidermis 
and outer 2-3 layers of the cortex, whose cells have 
colourless and comparatively thin walls ; b. and c. are the 
middle and inner zones respectively of the cortex, and 
consist of brown-walled sclerotic tissue, which is very thick- 
walled in proportion to the size of the lumen in b ., and less 
so in c. There is no very sharp line of demarcation between 
b. and c ., so the limit taken in the diagram is where the 
sclerenchyma begins to be appreciably thinner walled. 
In most species the cortex consists chiefly of brown sclerotic 
tissue, of the kind so frequently found in the cortex of other 
Ferns. Thus the sclerotic tissue of the cortex of G. dichotoma 
is composed of long brown-walled fibrous elements with 
oblique end-walls, but divided into shorter elements by 
transverse septa. The walls of the fibres bear small oval 
pits. The length of the fibrous elements is however variable, 
as one piece of rhizome of the same species was found to 
have quite short sclerotic cells in place of the long fibres. 
Several species resemble G. flabellata in having the epidermis 
