164 CHEMICAL CONSTITUTION [BOOK n. 



vessel was acted upon in its different parts in a very peculiar 

 manner. The exterior enveloping membrane (the original 

 wall of the 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 gela- 

 tinous 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. 



" II. 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 become 

 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 



