166 CHEMICAL CONSTITUTION [BOOK n. 



altissimum, which had been preserved for seven months in 

 weak alcohol (of about 30), were coloured orange. The 

 spires here consist, however, of two parts, which on the plane 

 of the section could be easily distinguished, as in Arundo 

 Donax ; and I imagine that the spire in Pleurothallis consists 

 only of the inner original fibre. I was not able to institute 

 any experiments with fresh leaves of this plant, and have there- 

 fore not been able to decide this question with certainty. The 

 original cellular membrane remained here, as in the first-men- 

 tioned cases, colourless, and the layers of increase became blue. 



"VII. Opuntia monacantha gave the same results. In 

 all the cells which were completely converted into wood, 

 the additional layers, whether spiral or pitted, became of a 

 deep orange colour, those of the pith and bark blue, and the 

 primary cellular membrane still remained clear as water. 



" An Echinocactus gave the same result. 



"VIII. The wood of Betula alba and Populus tremula, 

 when submitted to the above manipulation, showed nothing 

 but pitted formations, the primitive membrane of which 

 remained colourless, whilst the layers of increase were coloured 

 dark orange. 



" IX. A five years' old shoot of the trunk of Pinus silvestris 

 gave, as regards the original walls of the cells, confirmation 

 of the former constant results. The layers of increase were 

 coloured orange, the cells of the bark and the youngest annual 

 rings light blue. 



" It is of course to be understood, that, by comparative 

 experiments on all these plants, I had previously satisfied 

 myself of the absence of starch in the cells in question. 



"The foregoing, though only preliminary experiments, 

 seem to indicate the following results : 



"1. Vegetable tissue consists of three distinct chemical 

 substances : 



a. The original membrane of the cells. 



b. The primary layers upon this. 



c. The secondary layers. 



"2. The first substance (1. a.) undergoes no apparent 

 change by a short boiling in caustic potash. 



" 3. The second (1. b.) by short boiling in the caustic alkali 



