1 44 LESSONS IN CHEMISTRY. 



during their growth, and thus " the destruction of an existing 

 generation becomes the means for the production of a new- 

 one ; death becomes the source of life." 



216. If you recollect that the great bulk of every plant is de- 

 rived from the air, you will readily understand, that by burying 

 in the soil the crops produced upon it, you will not merely 

 restore the matters which they had abstracted during their 

 growth, but increase its natural fertility by adding to it the 

 elements which they had appropriated from the inexhaustible 

 storehouse of the atmosphere. The plants selected for the 

 purpose of being ploughed in are such as draw largely upon 

 the air for their nourishment, and which can be made at Httle 

 expense, in a short time, to produce a large crop of leaves 

 and stems. It is usual to turn them into the soil just before 

 the period of flowering, as at that time they are found to 

 contain the largest amount of useful matters. But besides 

 increasing the amount of organic matter in poor soils, much of 

 the beneficial effects of green manuring is to be attributed to 

 the mineral matters contained in the decaying plants. Thus, 

 when a crop of grass is ploughed down, the inorganic matters 

 which the deeply penetrating roots had extracted from the 

 subsoil, are transferred to the comparatively exhausted surface, 

 and brought within the reach of the succeeding crop. In 

 Ireland, though crops are rarely cultivated with the design of 

 being used as manure, yet the application of various kinds of 

 vegetable matter to the soil, is among the most important 

 means employed to maintain its fertility ; thus the sea- weeds 

 or wrach, which are found in so great abundance on our 

 coasts, and the deposits of vegetable matter in our bogs, are 

 used in every part of the country where they can be obtained. 



217. Sea-weeds. — These plants have long been employed by 

 the farmers on the coasts of France, Scotland, and Ireland ; and 

 as analysis shows that they contain all the ingredients which 

 our crops require, they must be capable of contributing to the 

 fertility of any description of soil. In many districts in 

 Ireland, no other manure than "sea- wrack" is applied, and 

 by its assistance the land is enabled, year after year, to pro- 

 duce the most exhausting crops. Sea-weeds are frequently 

 employed for dressing meadow lands, and are found greatly 

 to improve the quality of the grass; they are also formed 

 into composts with farm-yard manure, and, as they contain 

 a considerable amount of nitrogen, they rapidly ferment, and 



