44 



the district, expecting that by investigating those specimens, I might be able to 

 put the question to nature in a proper manner, and receive a correct reply. In 

 this I was not disappointed. 



Having weighed a given portion of the gorse, and fern, I burned off the 

 organized elements, and having weighed the residue of each, I found that the fern 

 left of ashes per 100 parts, 8'G, and the gorse 5'0. The fern contained 7 per cent, 

 of silica, the remainder being carbonate of lime and magnesia, with traces of 

 peroxide of iron and alkaline chlorides. The gorse contained 5 per cent, of ashes, 

 and was composed of peroxide of iron, carbonate of lime, and magnesia, a little 

 silica, and a trace of the alkaline chlorides ; the iron was in greater abundance 

 than in any other plant I have examined, though I believe it was not necessary to 

 the healthy development of this plant. The analysis of the soil showed that it 

 contained besides a great deal of soluble silica, an unusual proportion of organic 

 acids, such as humic acid, arising from the decay of a large projjortion of vege- 

 table matter in the soil. 



The analysis of the lime showed that it was similar to lime generally found 

 in this district. I had here a plain and satisfactory solution of the problem ; first 

 it was evident that silica was the chief inorganic food of the fern, and it abounded 

 in the soil, and from the quantity of carbon compared with the inorganic elements 

 in the gorse, it was clear that besides the portion of carbon supplied by the 

 atmosphere, this plant must take a large proportion from the soil, and the soil 

 was rich in carbon, in a state of transition into carbonic acid. Now if the lime 

 possessed the property of precipitating in an insoluble state the indispensable food 

 of these plants, the cause of their destruction was at once plain. By direct 

 experiment I found that lime had the property of precipitating soluble silica in 

 an insoluble form, and of hastening the progress of the decomposition of 

 carbonaceous matter, in order to form carbonic acid, for which the lime had a 

 great affinity, and by this means the lime was converted into the insoluble 

 carbonate, thus locking up for a time the food of these plants, and producing their 

 decay, and, remaining inert in the soil until it was rendered soluble by a double 

 dose of carbonic acid, it would descend into the subsoil and render a fresh supply 

 of lime again necessary. Guano would not produce this effect, for its value being 

 dependent upon the amount of volatile and fixed alkalies, as well as the phos- 

 phates, it would not convert the carbonic acid or silica into their insoluble 

 modifications, or combinations, but would have a tendency to dissolve a greater 

 portion of the silex, and set free a larger portion of carbonic acid. I have stated 

 that the quantity of iron I found in the ashes of the gorse was no proof that 

 iron was a necessary ingredient to the food of gorse ; I would rather consider 

 that it was carried into the circulation of this plant as an adventitious circum- 

 stance, being rendered soluble by the carbonic acid in abundance in the soil, and 

 the fixation of the carbon and liberation of the oxygen left the iron insoluble 

 in the tissues of the plant ; in this way can we account for a greater portion of 

 lime or magnesia existing in some plants in one locality than another. 



The question was proposed with a view also to ascertain whether or not some 

 other substance could supply the place of lime at less cost, and after repeated 



