CHEMICAL SCIENCE. 279 



soil ; the darkest colored lands are generally the highest in tempera- 

 ture ; hence the advantage of vegetable mould ; while deep, light 

 sands, and clay, which turns almost to stone in dry weather, weary and 

 vex the cultivator by their unprofitableness. It is to be remembered, 

 however, that soils which have the highest temperature of their own, 

 may not be those most susceptible of receiving heat that is, from 

 the sun, because some lands are warmed by the springs that irrigate 

 them. Here we have an explanation of the phenomena of certain 

 soils which are warm in winter and cool in summer. The application 

 of humus evolves heat by the process of combustion ; and sand, lime, 

 clay, and humus, are the combinations needed, the clay being in a 

 proportion of from 40 to 50 per cent. ; if less than 10 per cent, the 

 land will be too light and poor. 



Although Schleiden's views apply chiefly to the practice of German 

 agriculturists, they will be found to bear on the whole science of cul- 

 tivation. In summing up he insists strongly on the necessity for 

 selecting good seed ; that from a barren soil, he observes, is likely to 

 be more true to its kind than from well-manured land. Also, that the 

 time of sowing should be adapted to the requirements of the plant ; 

 rye and barley, for instance, should be sown in drier weather than oats. 

 And it will surprise many to read, that he advocates a less frequent 

 use of the plough. He holds ploughing to be " a necessary evil, one 

 to be employed only so far as necessity requires ; " because, by the 

 two frequent loosening of the soil, the decomposition of humus is so 

 rapid as to overbalance the benefit supposed to arise from exposure to 

 the atmosphere. He shews, too, that covered fallows are in most cases 

 preferable to naked fallows, as the latter tend to waste the valuable 

 qualities of the soil ; while, in a field sown with clover, the quantity 

 of humus and carbonic acid is increased by the leaves preventing 

 evaporation. Naked fallowing is to be adopted only when the soil 

 cannot be loosened in any other way ; but there is to be no stand-still ; 

 " the notion of rest, so prevalent among cultivators, is clearly wrong 

 except it be rest from the destructive influence of the plough ; " and 

 always must it be borne in mind, " that manures do not act immedi- 

 ately on vegetation by means of their organic contents, but by reason 

 of the inorganic substances which they involve." 



Such is a brief outline of some of the views of one who holds a hio-h 



j^i 



position among men of science ; and though in some particulars they 

 may seem to be at variance with practice in this country, there is much 

 in them worthy the attention of intelligent cultivators. It is remark- 

 able how different branches of science help in advancing the question, 

 and facts arise in support of the philosopher's theories. By a recent 

 inquiry into the amount and nature of the rain-fall at the observatory, 

 Paris, it has been proved, that from the 1st of July, 1851, to the end 

 of 1852, the quantity of azote combined therewith was omitting 

 fractions-- 22 kilogrammes per acre, being 12 kilogrammes in the 

 form of azotic acid, and 10 kilogrammes of ammonia. The quantity 

 of unconabined ammonia in the same time was 13 kilogrammes per 

 acre ; and of uncombined azotic acid, 46 kilogrammes. In the months 



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