70 NUTRIENT SALTS. 
protoplasm in construction, and in the storage of materials. The annexed table, 
which gives side by side analyses of the ash of branches of the Yew (Taxus baccata) 
with their leaves attached, illustrates the replacement of calcium by magnesium :— 
Ash from branches and leaves of the Yew from 
| Serpentine. Limestone. Gneiss. 
Rilicic Acid re ease | 38 3:6 37 
DSULPHUPICHAICIO  eccsemssessnccueeenestctsectmrirs | 19 16 19 
IPHOSPHOVICPA CIC) esce-soaceseescaeatesesn-ascene | 83 55 42 
ERS Ob eG yore 271 17 06 
Dim Genes = Stabs causes successes anes seems sence 16:12 36°1 4 30°6 er 
IMagnesia, <.cscasaascuctseecct esse ces es esccenksese 227 | 38:8 51 (412 5:7 (363 
IRotash ticinssesctesssntastoccececs tered een aan 29°6 21°8 27°6 
CarbonicvAcidireccnccs:sesesscscecuescdeaveeres 141 23°1 24.4 
Traces of Manganese, Chlorine, &c.,......... — | —_ E= 
Totalsy ee 99:6 | 98:5 98:7 
The Yew occurs in Central Europe on very various mountain formations, chiefly on 
limestone, but not infrequently on gneiss, and occasionally on serpentine rocks. 
On comparing the quantities of calcium and of magnesium in the ash of yews, grown 
on lime and on gneiss respectively, with those yielded in the case of serpentine for- 
mation, we find that magnesia preponderates considerably in weight over lime in a 
yew from serpentine rocks (which are in the main a compound of magnesia and 
silicie acid), whilst the proportion between these two salts is reversed in a yew 
grown upon limestone. The obvious inference from the table is that, in plants from 
a serpentine ground, lime is to a great extent replaced by magnesia. This is fur- 
ther supported by the circumstance that if lime and magnesia are counted together 
the resulting numbers are very near one another, namely 41:2 per cent of the ash 
for limestone, 38°8 per cent for serpentine rock, and 36°3 per cent for gneiss. 
But all these phenomena observed in connection with the selection of food-salts 
are not nearly so surprising as the fact that plants are also capable of singling out 
from an abundance of other matter particular substances, which are of impor- 
tance to them, even from a soil containing them in barely perceptible quantities, and 
of concentrating them to a certain extent. As has been shown above, nearly a 
third of the ash of the white water-lily is composed of common salt. One might, 
therefore, suppose that the water in which water-lilies flourish contains a particu- 
larly large quantity of common salt. But nothing of the kind is the case. The 
bog water which bathed the stem and leaves of this specimen only contained 0°335 
per cent of common salt, and the mud through which the roots straggled contained 
only 0:010 per cent. 
No less astonishing is it to find Diatomacex, with cell-membranes, as above 
mentioned, sheathed in silicie acid, existing in water which contains no trace of 
silicic acid. Above the Arzler Alp, in the Solstein chain near Innsbruck, there is a 
spring of cold water which falls in little cascades between blocks of rock. The 
