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Scientific Memoirs by
and the lamina may be described as consisting of two layers of epidermis kept
apart by enormous numbers of large idioblasts and here and there con-
nected by bands of parenchymal tissue (Plate II, fig. 5). In the upper half of the
thickness of the lamina there is a dense, sub-epidermal stratum of parenchyma
interrupted by comparatively small substomatic spaces (Plate II, fig 3) and by the
thick shafts of the idioblasts. In the lower half parenchymal tissue is at a
minimum, only appearing in the form of thin partitions traversing a series of
enormous spaces immediately above the inferior epidermis and crossed by the
lower extremities of the idioblasts. The latter consist of a shaft, the upper
extremity of which is in contact with the under-surface of the superior epi-
dermis, and of a series of terminal rays, the tips of which extend to the upper
surface of the inferior epidermis. In Nymphœa lotus and rubra there is a
well-defined stratum of palisade cells, and the idioblasts are neither so abun-
dant nor do they extend so completely through the thickness of the lamina as in
Nymphœa
stellata. They do not extend from one epidermal surface to the
other, for while their bases are in direct relation to the under-surface of the
superior epidermis, their rays, which are enormously elongated horizontally,
do not reach the upper surface of the inferior one, but are spread out at some
distance above it.
On making vertical sections of affected leaves of Nymphœa stellat1 a t h e
yellow patches on the surface are found to correspond with areas of tissue occu-
pied by mycelium and spores of a parasite. The mycelium consists of very
delicate, sparsely septate branched filaments, and small, simple, bud-like
haustoria projecting into the interior of the cells of the host (Plate II, fig. 6).
So very delicate and slender are the filaments that it is only by means of staining
them that their presence in the tissue can be detected, and here, as is the case
with so many fungal mycelia, Spiller's purple is by far the most efficient staining
agent. The mycelium is mainly distributed in the dense, sub-epidermal paren-
chyma, but now and then a stray filament may be encountered in the great in-
ferior system of intercellular spaces. Where the mycelium enters the substoma-
tic spaces, the filaments become considerably thicker and ultimately produce
masses of spores (Plate II, fig. 4), which are thus absolutely limited in dis-
tribution to the upper half of the thickness of the lamina.
The sporiferous filaments are abundantly branched and densely filled with
vacuolate protoplasm. The ultimate twigs each produce a single spore, which
makes its first appearance as a fusiform dilatation of the parent filament a little
below the extremity (Plate II, figs. 4 and m). The dilatation is atfirst occu-
pied by a vacuolate protoplasm continuous with that in the distal and proximal
portions of the filament. It gradually increases in size and ultimately becomes
almost spherical in some cases, and as it grows it invades the terminal portion of
the filament, which thus becomes reduced to a mere process connected with the
distal side of the dilatation. This process is at first hollow and contains proto-