CHAP. I. 
ELEMENTARY ORGANS. 
291 
cell) was apparently not in the slightest degree altered ; it 
was still firm, close, transparent, and clear as water. The 
fibre itself consisted of two component parts ; namely, of a 
(primary?) fibre lying close’ to the wall of the cell, and of an 
enveloping membrane surrounding the fibre on the three free 
sides in the interior of the cell. The caustic potash had 
coloured this enveloping membrane of a somewhat darker 
yellow, otherwise it was firm and apparently unaltered ; the 
primary fibre, on the contrary, was changed into a gelatinous 
mass, so that on the plane of the section it was swelled up 
into a pretty considerable elevation. Unfortunately I did 
not follow up or vary these interesting observations, till after 
I had thrown away the remainder of the fresh piece of the 
Donax. 
“ IL The next experiment I instituted was on the leaves of 
Pleurothallis ruscifolia. The greater part of the cells of this 
plant contain beautiful spiral fibres, which appear to grow 
firmly against the walls of the cells. These fibres are all 
very broad and flat, like a riband, their thickness varying 
according to their position. Those cells which are situated 
vertically, immediately under the epidermis of the under side 
of the leaf, contain a thicker fibre than the less regularly 
formed cells, which are separated from the latter by a layer 
of green parenchyma, and from the upper epidermis of the 
leaf by an occasionally broken layer of colourless cells, mostly 
with plain walls. After I had boiled fine sections of this leaf 
in caustic potash for a few minutes, and again examined them, 
I found that the spires of the first-mentioned layer had be- 
come entirely separated from the walls of the cells. Under 
the simple microscope I could easily tear up single cells with 
a needle, and isolate the whole spiral fibre uninjured. More- 
over, all the fibres were tumefied, and had acquired a gela- 
tinous appearance from the action of the caustic potash. I 
now added a drop of sulphuric acid, which neutralised the 
potash with effervescence, and I then added an alcoholic 
solution of iodine. On again bringing the object under the 
microscope I was most agreeably surprised. All the spiral 
fibres, according to the varying thickness of the section (hence 
the unequal action of the caustic potash), appeared of different 
u 2 
