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tomed to examine licliens^ it will be at once apparent that 
these are really portions of lichens^ either of its true substance^ 
or of the mealy portions called sori found on the surface 
of many. These meal-like grains are situated on the exterior 
of many old lichens, generally of the colour of the parent 
frond ; under the microscope they are opaque, but when com- 
pressed under the glass they are seen to be composed of from 
one to many green cells ; around and amongst which there are 
to be noticedcolourless tortuous fibres (figs. 2, 3). These are 
the fibres which form the major part of lichens, so that these 
sori contain the elements of these plants, though not as yet 
assuming the shape of the parent. 
Now the green cells, before mentioned, to be obtained from 
snow, in the interior of lichens, and in their sori, are, so far as 
the eye can distinguish, in form, mode of growth, &c., identi- 
cally the same. 
But further, they are not distinguishable from the mature 
round cell of the Chlorococcus, the green plant already noticed 
as occurring so extensively on barks of trees, &c. Besides, if 
the green cells of most of the lichens, as Parmelia, Lecanora, 
&c., are kept moist, or in water, and watched under the micro- 
scope, they will be seen dividing (fig. 3) exactly as Chlorococcus, 
shown in fig. 1 . An easy mod.e of observing these changes is 
to place a small portion of the object on a glass slide with a 
drop or two of water, covering it over with the ordinary thin 
glass. Over this place a watch-glass, by which means eva- 
poration is much retarded ; a little water should be supplied as 
often as required. The watch-glass being removed, the slide 
can be placed on the stage of the microscope. 
Thus, then, we find that the green cells, or gonidia as they 
are called, of the lichens, are imitators of the Chlorococcus. 
But there are others. On the ground at the foot of palings, 
trees, and walls, in the early part of the year, may be seen 
wavy strips of light-green growth of varying width, frequently 
narrower at one end than at the other. This growth has been 
known by the term Prasiola.-’^ It was the object of one of 
my papers to point out that this Prasiola had been during dif- 
ferent stages of its increase placed in three distinct genera 
wide apart. For continuous observation easily discovers 
that it springs first from round green cells (fig. 1 a). These 
grow into filaments in the mode already shown, having one 
row of cells. These again divide laterally, so as to make a 
filament of two rows, which, repeating the process, make a 
tapering wavy band. However, the point with which we are 
concerned is this; that the filaments spring from cells which 
entirely resemble the Chlorococcus first mentioned, both in 
colour, size, form, and mode of division. Besides which, the 
VOL. TV. — NO. XV. 2 A 
