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 S), 

 &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 

 proof, 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 

 promote 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 phenomenon, 

 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 



