Relation to Chalk and Mineral Salts. 
75 
strated by washing free from the cuprous solution and treating with 
ammonia; the leaves, and especially the thicker stems, take on a marked 
blue-green colour. 
II. Localization of the Acid Compounds. 
Baumann and Gully express the opinion that the walls of the hyaline 
cells are the chief seat of the colloids, but they do not give any experi¬ 
mental evidence in support of this view. The attempt was made to find 
out whether the compounds were located in any particular position in the 
plant. 
The leaves were carefully teased off a number of Sphagnum plants, 
and the leaves and leafless stems placed separately in 5 per cent. NaCl 
solution. Both gave a strong acid reaction. 
Quantitative determinations show that the stem is very slightly more 
active than the rest of the plant. As the method employed was the same 
in all quantitative determinations it may be described here. It was found 
impossible to treat directly with sodium hydroxide, as the resulting solution 
was frequently too dark to admit of accurate titration. Consequently the 
method of estimating the acid liberated from a salt was employed. 
10 per cent, calcium acetate is the most advantageous salt; according to 
Baumann and Gully the amount of acetic acid set free is equal to 95 per cent, 
of the acidity of the Sphagnum , as indicated by direct treatment with sodium 
hydroxide. The solution obtained is almost colourless, and may be accu¬ 
rately titrated with phenolphthalein and hydroxide. 1*5 grm. of dry 
Sphagnum was shaken for six hours with 100 c.c. of the solution, and the 
acid determined in the liquid strained off through muslin. The acid is 
expressed in grammes of acid hydrogen per 100 grm. of dry Sphagnum. The 
figures are thus comparable with those of the former investigators which are 
expressed in the same way. 
Two lots of Sphagnum cymbifolium were treated in this way ; the 
one (a) consisted of small branches and leaves, the other ( b ) of carefully 
selected stems. The acidities were : 
(a) 0*080, 
(b) 0*085. 
The difference is small, but it was obtained in four further experiments. 
The slightly greater acidity of the stems might be referred to the greater 
thickness of the cell-walls. 
That the acid reaction is not connected with the life of the plant 
scarcely needs proof; it is given by plants in the fresh state, and by plants 
dried for several hours at temperatures of over ioo°C. From this, however, 
it does not follow that the reaction is due to the wall rather than to the 
cell contents. 
