FUNCTION.] OF TISSUES. 165 



the unequal action of the caustic potash), appeared of different 

 shades, from claret colour to the deepest violet. In those 

 places where the section was not more than a single cell in 

 thickness, a difference between the fibres in the above men- 

 tioned layers was visible, inasmuch as those of the under side 

 of the leaf (the thickest), even where they were most deeply 

 coloured, did not appear of a pure violet colour, but redder, 

 somewhat as if there had been a slight addition of orange. 

 These fibres were also evidently less tumid, and the bound- 

 aries were more clearly defined. Those in the middle of the 

 leaf, on the contrary, appeared quite gelatinous, and were 

 coloured of a light blue. The membrane of the cells was in 

 all cases clear as water, and colourless. This was not all : 

 those cells which contained no spiral fibres, and which before, 

 when magnified 230 times, appeared to consist of quite simple 

 walls, even those of the green parenchyma, appeared now 

 completely pitted ; the primitive membrane and its pits were 

 clear as water, and colourless, whilst the pits of the thickening 

 layer were of a violet colour. 



" III. I now took for comparison a woody stalk of Rosma- 

 rinus officinalis, and treated it in precisely the same manner. 

 The result differed slightly from the above. The cells of 

 the pith are here very thick-sided and pitted, as are also the 

 exterior cells. The wood consists of the medullary sheath, 

 of spiral vessels, and of prosenchymatous cells, the walls of 

 which are just like the woody cells of very young coniferous 

 wood. Here, in every part except the youngest annual rings, 

 the original membrane (even of the spiral vessels) was not 

 coloured, whilst those parts superposed, and even the spiral 

 fibres, were deep orange. The cells of the youngest annual ring, 

 on the contrary, appeared slightly pitted and very pale blue. 



" IV. A species of Pelargonium, when submitted to the 

 same action, gave the same results, only that the thin-walled 

 but pitted exterior cells were also coloured blue. 



" V. In the Teltow Turnip and Carrot, the primitive walls 

 of the cells remained colourless ; the incrusting layers of the 

 same became blue ; whilst, on the contrary, the fibres of the 

 spiral and reticulated vessels became deep orange. 



" VI. The spiral fibres, in the cells of a leaf of Oncidium 



