KNOWLEDGE OF MONOCOTYLEDONOUS SAPROPHYTES. 169 
Tegions of the scales have brown walls and contain hyphe. 
Raphide-mucilage sacs occur in the mesophyll of the scale. 
The vascular bundles, at the base, are nearer the upper (inner) 
face of the leaf, and are separated from the inner epidermis by one 
or two layers of mesophyll. The bundle is invested with a sheath 
of sclerenchymatous fibres, which is more strongly developed on 
the side remote from the inner epidermis. The bundle contains 
xylem and phloém, but there is relatively little phloóm. Within 
the sheath on the upper (inner) side are some parenchymatous 
cells longitudinally elongated which contain starch. Within 
these lie the xylem, commencing with narrow spiral vessels and 
followed by tracheides. Parenchyma-cells separate the xylem 
from the phloém with sieve-tubes. Separating the phloém from 
the sheath again is a more or less complete layer of parenchyma- 
cells which contain starch. (Starch occurs in no other cells of 
the scale.) In small vascular bundles the phloém is represented 
by a mass of very narrow elongated parenchyma-cells. 
Following the scale up towards its apex, certain remarkable 
changes in structure are visible. On the side towards the inner 
epidermis gaps arise in the sclerenchyma-sheath, and single subepi- 
dermal cells are changed into broad storage-tracheides which are 
connected with the xylem of the bundle. Ascending higher, the 
bundle-sheath disappears and there is developed within the inner 
epidermis a complete network of these tracheides, which are con- 
nected with the xylem of the bundles. In transverse section this 
extrafascicular system of tracheides seems to extend like a pair of 
wings from each bundle, and meet the wings from the adjacent 
bundles. These tracheides are elongated longitudinally and not 
directed at right angles to the epidermis. There are considerable 
gaps in the network of tracheides which are occupied by ordinary 
mesophyll-cells. The inner epidermis immediately outside the 
hypodermal network of tracheides has thin feebly cuticularized 
walls. Nearer the apex and margins of the scale this hypodermal 
system disappears and the inner epidermis acquires thick walls 
with a conspicuous cuticle. 
The hyphæ penetrate the outer epidermis and the regions near 
the tip and margins, more abundantly than they do the thin- 
walled part of the inner epidermis. This may be simply because 
these parts of the leaves are more exposed. In one bract hyphe 
had penetrated the inner epidermis and traversed a series of hypo- 
dermal tracheides, causing disorganization of the cells attacked. 
