160 UR sen LEIDEN'S THEORY OF AGRICULTURE. 



latter, to protluce which is the great office of the organic matter 

 ill manure. The manure, however, made upon a farm will not 

 suffice for this, without there is a proper proportion of meadow or 

 of artificial grasses. Other physical conditions, as temperature, 

 looseness of soil, are also promoted by this substance, which liow- 

 ever on strong clays may, to a certain extent, be replaced with 

 sand, and on loose sands with clay, where it is profitable to do so. 



C. The regulation of water or draining is absolutely indispen- 

 sable for good cultivation, while, on the other hand, the freest 

 irrigation is of immense advantage. The difference arises from 

 the state in which the water is which comes in contact with the 

 roots of the plants. The poorest vegetation exists in moors and 

 peatbogs, which are constantly saturated, wldle the richest is found 

 in alpuie meadows constantly irrigated. The difference is, that 

 in the one case the water is stagnant, and in the other constantly 

 changed. Plants require but little sulphur, and consequently 

 sulphuretted hydrogen, supposing that they receive their sulphur 

 in this form. Sulphates in contact with decaying organic substances 

 soon unite with them, and tluis sulphuretted hydrogen is generated 

 in such quantities as to be destructive to many plants. 



D. A few remarks on rotation of cropping must close our 

 abstract. 



Experience has shown that fallows may be in a great measure 

 dispensed with by a system of rotation, including clover. The 

 object of science is to show in what way this is explainetl by the 

 nature of plants, and inasmuch as improvement is impossible, or 

 at least accidental, without knowledge, such inquiries have their 

 practical side. It is on the cultivation of clover that the main 

 advantage of rotation depends, the object of it being to increase 

 the quantity of humus ; and it is to be observed that in the pub- 

 lished tables a very important part of the accession derived by 

 the field is neglected, namely, that from the leaves which are 

 constantly withering and falling off, which amount perhaps to 

 twice or thrice as much as what is carried away. 



Wheat, like other cereals and grasses, will succeed without 

 humus, provided the requisite moisture be kept up, but where 

 this is not possible there must be either a verj' favourable clay, 

 or the groiuid must be very rich in hiunus ; but, in consequence 

 of their thin leaves and slender hollow stem, they cannot take up 

 a great quantity of moisture at once in anticipation of a dry time, 

 and therefore they require an uninterrupted supply of moisture, 

 which must be afforded by absorption from the atmosphere by 

 means either of the clay or vegetable mould. 



There are two points to be distinguislied Mith respect to rota- 

 tion. First, it may be regarded as a whole, as a method of culti- 

 \ ation by which cloxer takes the place of fallow, and by u hich a 

 greater produce of cereals is possible ; and this leads to the 



