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CELLS AND CELL PRODUCTS 217
slices and of dissolving away the lime enabled them to see the tissues in
their relative positions. In these immersed lichens, as described by them and
by previous writers, and more especially in calcicolous species, the gonidial
zone of Protococcaceous algae lies near the surface of the rock, and is
mingled with delicate, thin-walled hyphae which usually do not contain oil.
The more deeply immersed layer is formed of a weft of equally thin-walled
hyphae, some of the cells of which are swollen and filled with fat globules.
These oil-cells may occur at intervals along the hyphae or they may form
an almost continuous row. In addition, strands or bundles of hyphae (Fig.
1 1 8) containing few or many oil globules traverse the tissue, and true
Fig. r 1 8. Biatorella (Sarcogyne) simplex Br. and Rostr.
a, sphaeroid oil-cells ; b, strand of oil-hyphae from
10-15 mm. below the surface, x 585 (after Lang).
sphaeroid cells are generally present. These latter arise in great numbers
on short lateral branchlets, usually near the tip of a filament and the groups
of cells are not unlike bunches of grapes. Sometimes the oil-cells are massed
together into a complex tissue. Hyphae from this layer pierce still deeper
into the rock and constitute the rhizoidal portion of the thallus. They also
produce sphaeroid oil-cells in great abundance (Fig. 119).
Fig. 119. Biatorella pruinosa Mudd. a, complex of sphaeroid
oil-cells from lomm. below the surface; t>, hypha of sphaeroid
cells also from inner part of the thallus. x 585 (after Lang).
In the immersed