8o 
Skene .— The Acidity of Sphagnum and its 
were so dark or so ruddy that any approach to accuracy was quite out of 
the question. With calcium acetate, on the other hand, accurate values 
may be almost always obtained. 
There is reason to believe that the acidity of a single sample varies 
throughout the year. If the acid compounds really act as absorbers of 
salts, which are then used up in growth, continued absorption during winter, 
when growth is at a standstill, will result in a relatively smaller acidity. 
A sample of .S. recurvum gave an acidity of 0*0517 in early April. A large 
tuft was placed in a 2-litre bottle with distilled water, and after six weeks 
had increased in length by 2-3 cm. The new growth was cut off and the 
acidity determined in it and in the older parts; the latter gave 0*0678, the 
former 0*0758. This indicates that during growth minerals are actually 
removed from the older parts ; while, growing in distilled water, the young 
shoots, not being able to absorb bases, have a very high acidity. But it also 
shows that in normal conditions the acidity will vary greatly according to 
salt supply and rate of growth, and that consequently the difficulty of 
obtaining a value characteristic of a species is increased. Paul’s Table (IV) 
should thus be taken with some caution. The order in which Table VI 
places the species does not agree well with that of Paul, but it might be 
materially altered by selecting individual determinations ; in any case 
a comparison is not profitable, as the number of species studied in common 
is not sufficiently large. 
Tacke and Siichting state that the acidity of Sphagnum cannot be 
increased by washing out. I obtained an increase in every case; the 
discrepancy may be due to the use of ordinary distilled water containing 
only a small quantity of carbon dioxide by these authors. 
V. Sphagnum and Chalk. 
The relation to calcium carbonate maybe discussed under two different 
heads : (a) Is the sensitiveness different in the different species ? ( b) In 
what does the toxic action of chalk consist ? 
( a ) If we place 5 . rubellum and 5 . contortum in water containing 
100 mg. of calcium carbonate to the litre, we find that in a day or two the 
former has turned a dirty blackish colour, and that after a fortnight or three 
weeks it has died and fallen to pieces without having grown in the least; 
contortum , on the other hand, remains bright green, exhibits geotropic 
movements, and adds considerably to its length. This illustrates the fact 
that different species are sensitive in different degrees. The relation of 
growth to calcium carbonate was investigated more exactly in the case 
of three species of widely different acidity : 
5 . contortum , 0*0276 0*0597 {primary) 
S. recurvum , 0*0517 0*0707 ( primary) 
S. rubellum , 0*0863 
