270 Meyen’s Report for 1839 on Physiological Botany. 
tical value, but also contains additions to our science. In 
the introduction we first obtain a view of the theory which 
was followed by the author in the compilation of his work. 
Under manure, he understands everything which belongs 
either to the means of nourishment of plants or to their 
chemical composition. Besides carbon, oxygen, and hydro- 
gen, the author mentions eleven others, viz. lime, magne- 
sia, soda, potash, alumina, silicic acid, iron, manganese, chlo- 
rine, phosphoric acid, and sulphuric acid, which are also to be 
considered as manures, because they are found more or less 
in all plants; and indeed, says the author, “ they are really 
manures ; for if we strew a boggy or marshy soil with quartz 
sand, we soon see that plants, particularly grasses, grow better 
there! The manures are divided into such as merely nourish 
and strengthen the plants, as gypsum, salt, copperas (Fe §), 
&c., and such as not only nourish but also act as solvents on 
several of the constituents of the soil, which are thereby con- 
"verted into substances suitable for the nourishment of the 
plants ; and to this group are reckoned dung, ashes, marl, &c. 
The generally received opinion, that minerals, as gypsum, 
nitre, copperas, &c. act as stimulants on the growth of plants, 
is considered by the author to be perfectly incorrect; as 
roof, he mentions that the completely putrified urine of 
horned cattle consists solely of mineral substances, dissolved 
in from 90 to 92 per cent. water, and that this is nevertheless 
one of the most excellent manures. Moreover, the manuring 
with saltpetre is adduced by the author, as a proof that mi- 
neral substances are to be considered as true manures, of 
which often only minute quantities are necessary in order to 
romote to an extraordinary degree the growth of plants. 
The author has here adduced two examples, which certainly 
appear very striking; but he has forgotten to add that the — 
carbonate of ammonia in the urine is a substance which is 
completely decomposed in the interior of plants, and that its 
constituent elements belong to the principal components, or 
rather to the most excellent kinds of food of plants, and by 
this the principal argument which he brings forward in sup- 
port of his theory is done away with. As far as concerns 
the manuring with nitre, it appears to me as if we were still in 
perfect darkness as to the explanation of the phznomenon, 
and that this cannot, at any rate, be used as a proof in favour 
of the author’s theory. We know indeed that nitre may 
be contained in plants, but we do not know either how much 
of the nitre taken up from the soil is decomposed into its ele- 
ments, or how much remains undecomposed ; the acid of the 
nitre is probably again resolved into its elements, as in the 
