AND LIFE-HISTORY OF A TROPICAL EPIPHYLLOUS LICHEN. 89 
mycelium, and that the porcellaneous white matrix of the complete lichen consists of the 
same Algal thallus completely invested by dense masses of the Fungus-hyphe, which 
in turn produce their fruit-bodies as the shining black dots above referred to. The 
grey-green stage is particularly interesting, as it allows both Alga and Fungus to be 
observed in vigorous conflict (Pl. XVIII. fig. 4 &c.). Having premised this, it will be 
convenient to describe in order the Alga, the Fungus, and the Lichen. 
THE ALGA. 
If a specimen of the orange-red spots be removed with a razor from the upper side of 
the leaf of Michelia, and magnified 30 or 40 diameters, it is found to consist of a discoid, 
lobed, or branched thallus, formed of cells symmetrically arranged in rows, radiating 
from one or more centres to the periphery of the disk or its lobes (Pl. XVIII. figs. 2 & 5; 
Pl. XIX. fig. 16, and Pl. XX. fig. 89). The structure calls to mind that of the 
thallus of Coleochete (** Phycopeltis,” “ Phyllactidium" &c.), and, as will appear shortly, 
is essentially similar in character, mode of growth, &c.* 
In Во. 5 а is drawn a portion of a terminal lobe of the thallus, seen from above by 
transmitted light; and at с the radial arrangement of the closely appressed cells is 
rendered quite evident. This arrangement results from the apparently dichotomous mode 
of division of the cells as the periphery of the thallus advances and extends itself (с/. 
also Pl. XX. fig. 40). Each vegetative cell of the thallus is found to consist of a firm 
cellulose wall, enclosing abundance of cell-sap (in which granules and oily particles may 
be floating), and a mass of protoplasmic and fatty contents, some of which are soluble 
in alcohol and ether. These may be coarsely granular, with large, orange-red, oily drops 
scattered throughout ; or a finely granular or cloudy green matrix may contain a more 
or less sharply defined sphere of orange-red and coarse-grained bodies (figs. 5 & 6). In 
the latter case the fine-grained matrix is distinctly tinged with an apple-green diffused 
colouring-matter, resembling chlorophyll, and no doubt consisting of that substance. On 
adding potassic hydrate, the (now yellowish) matrix may become more evident. The 
relative proportions of this green substance and the red oil globules in the cells, 
determine the general hue of the thallus (cf. Pl. XVIII. figs. 4, 5, 6, Pl. XIX. fig. 12, 
Pl. XX. fig. 42, &c.); and it appears certain that the two colouring-matters are convertible 
one into the other, much as the red and green colouring matter in Euglena, Protococcus, &e. 
Such cells always contain abundance of starch ; and a vigorous thallus, such as is being 
described, becomes coloured with a deep indigo-blue tinge in most parts when iodine is 
added. Хо definite starch-granules could be discovered; and even the orange-red or 
yellow oily-looking masses absorb the iodine and become blue-black. Not only in these 
thallus-cells, but also in the hairs and zoospores to be described, does this reaction 
occur. 
І have not succeeded in discovering an undoubted nucleus in any of these cells. Тһе 
red spheres (figs. 5 & 6) often found are aggregations of oily drops and protoplasm, con- 
taining starch and other substances, and cannot be regarded as in any way of the 
nature of nuclei. 
* Points of analogy with the Chroolepidee will be discussed later. 
Q 2 
