A NEW GENUS OF PARASITIC ALGA. 803 
series of cells by transverse septa, and terminate superiorly either in blunt points or in 
more or less developed spherical capitella bearing a few large spore-like cells on short 
curved processes (Pl. XLII. fig. 2). The appearance of a mass of such filaments, with 
their transparent glassy walls and brilliantly coloured contents, is strikingly beautiful. 
Besides such filaments, numerous older ones are seen—some prostrate and colourless, 
others still erect and with coloured contents remaining in their cells and capitella, but 
with only empty spore-cases adherent to the latter. Some with more or less developed 
heads are also encountered, which are distinguished by the presence of greenish rounded 
masses adhering to them laterally, whilst in many the cell-contents, in place of being of 
an orange colour, are vividly green. 
On detaching such a pustule from the leaf, and examining it under higher powers, it 
is found to consist of a flattened subepidermal disk of radiating filaments, from which 
numerous ascending twigs arise, which, breaking through the epidermis, are developed 
into the fructifying filaments just described. Careful vertical sections of the leaves, such 
as may be obtained by means of paraffin as an embedding medium, show very clearly 
the arrangement of the various portions of the pustule and its relations to its host 
(Pl. XLII. fig. 8). 
Before proceeding further, however, it may be well briefly to describe the structure of 
the mature Camellia-leaf. On examining a good vertical section we find the entire thick- 
ness of the leaf to measure on an average about 0°3125 millim. Proceeding from above 
downwards, there is first a very dense layer of epidermal cells. These are colourless, 
flattened, and on treatment with iodine frequently show a very distinctly stratified 
structure in their walls. They have sinuous margins laterally and beneath, by means 
of which they dovetail into one another and into the irregularities of the subjacent 
stratum. This layer measures about 0:0100 millim. in its thicker and 0:0075 millim. in 
its thinner portions. The cells of the next stratum are also very thick-walled, and appear 
. on section as a series of cubes. They form a continuous stratum, about 0:02 millim. in 
thickness, and are distinguished by the small amount of their contents, and by hardly 
ever showing the presence of any chlorophyll. As a rule, in fact, they appear almost 
empty, containing only a peripheral layer of protoplasm, or in rare instances a small oil- 
globule. Beneath this comes a stratum composed of from one to three rows of prismatic 
elongated cells, measuring about 0°050 millim. in long diameter, and full of chlorophyll 
granules. The continuity of this stratum is interrupted by the intercalation of a series 
of very remarkable cells at uncertain intervals. These are the remains of a system of 
‘cells which at one stage in the development of the leaf form the greater part of its 
substance, and are gradually thrust aside and separated by the development of the 
common cells of the leaf-tissue. They are of great size, in some cases attaining a length ` 
of 0°25 millim., and a diameter of 0:035 millim. at their wider basal extremity. They are 
rendered very conspicuous by the great thickness of their walls, as well as by their 
colourless finely granular contents. They are usually only found proceeding from the 
upper towards the lower surface of the leaf, being inserted immediately beneath the 
subepidermal layer; but occasionally they occupy a reverse position, and are then - 
inserted on the inferior subepidermal layer. They are broad at the extremity of 
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