TBANSACTIONS OF SECTION B. 551 



of the essential ingredients of plants, he says that they ' may benefit or injure plants 

 according to the combination in which they are applied ; thus chloride of lime and 

 carbonate of magnesia are said to be plant-poisons, although composed of ingredients 

 which are beneficial in other forms, such as carbonate of lime, sulphate of magnesia, 

 chloride of potash, &c.' And again, ' As to magnesia, it may be put down quite as 

 a neglected substance in manures. Judging from examination of soils its appli- 

 cation is called for in many cases more urgently than most of the other essential 

 ingredients.' It is true also that Messrs. Lawes and Gilbert introduced 16-3 per 

 cent, of sulphate of magnesia ( = 2 per cent, of magnesia) into the mixed mineral 

 manures employed in their experiments at Eothamsted, and small quantities were 

 used in the trials of manures made in 1841 and 1842 in Scotland ; but one of the 

 most eminent authorities on the question of manures, M. Yille, whose work has been 

 justly received with much appreciation by agriculturists in America and England 

 as well as in his own country, does not think it necessary to introduce magnesia 

 into manures at all, not because he does not consider it to be an essential element 

 in vegetation, but because, as he states, 'it is found in the soil ' 'naturally,' and of 

 coiu'se he means in sufficient abundance for tJie requirements of plants. 



How far the accuracy of this opinion is borne out by the facts he cites is, I 

 think, open to question, and I therefore place the whole matter, almost in his own 

 words, before you, and it will form an appropriate introduction to my paper. 



M. Ville gives in his work the analysis, by Da-^-y, of six samples of earth 

 from different sources, 'all renowned for their fertility,' and states that ' all six 

 possess the same degree of fertility.' Now Sir Humphry Da^'y, in his work on 

 Agricultural Chemistry, gives the analysis of three of them, and of these he says 

 that one was from a hop garden, another from a ' good turnip soil, and a third 

 from an excellent wheat soil.' In none of the six samples, excepting that from the 

 'hop garden,' did Sir Humphry Da\'y find any magnesia, and in that he found 

 •7 per cent, of magnesic carbonate ( = '33 magnesia). M. ViUe gives also the 

 analysis of a soil from Chalons-sur-Marne, by M. Rivot, which showed only traces 

 of magnesia. At the same time they contained, with one exception (which had 

 only '6 of calcic carbonate), a fair proportion of lime, viz. from 4-7 to 57 '2 of calcic 

 carbonate. It is true that in the days of Davy methods of analysis were not so 

 accurate as at present, and that magnesia might have been, and most probably 

 was, present in some of the five samples in which it was not detected or noted by 

 Idm ; but the magnesic element must have been present in insignificant proportion 

 in comparison with the calcic. 



At the end of his work M. Ville gives tables for calculating the relative exhaus- 

 tion of soils under different crops, but in these tables no mention whatever is made 

 of magnesia as an element abstracted from the soil by plants, though it is an im- 

 doubted fact that the seeds of peas, beans, rape, and wheat carry off" a comparatively 

 lai-ge proportion of it. In 100 parts of the seed crop of wheat there are 12 parts 

 of magnesia and onlj' 4 of lime, and in the straw of this plant the quantity of mag- 

 nesia is about one-half that of the lime, yet M. Ville omits magnesia from his normal 

 manure for cereals, though lime, in the somewhat soluble condition of sulphate, forms 

 nearly one-half of the whole compoimd recommended for a wheat crop. And this 

 fact appears the more remarkable when we examine the experiments made with 

 the different mineral elements of plants by M. ViUe. With reference to these 

 experiments, he says : ' This time a fixed and invariable q\iautity of nitrogenous 

 matter was mixed with the [calcined] sand [soaked with distilled water] as a 

 constant ingredient, and all the other mineral ingredients were added by turns 

 except one. The experiments were repeated as many times as there were different 

 mineral ingredients, in order that each might be excluded in its turn, the deviation 

 between the crops obtained with the ten mineral ingredients and those in which 

 they were reduced to nine, being taken to indicate the degree of importance of the 

 suppressed ingredients. 



' Magnesia was submitted to the same method of exclusion. The defects were 

 as disastrous as in the case of potash. 



' There are some plants, particularly buckwheat, on which the effects of this 



