44 UR. SCHLEIDEN'S THEOKT OF AGRICULTURE. 



walls. We can form a notion of the content in silex from an 

 examination of domestic plants, though silex is by no means 

 characteristic of tliem, but rather of monocotyledons in general. 



100 Parts of Silex. Mean. 



Maize straw from Quartzose ground . . 9 



from Transition lime 



;;") «.^< 



ZoZtM»ipere«?/e from Quartzose ground . 2.5,11122 27 

 „ from Transition lime . . 19, 4-3 j ' 



In dicotyledons the result is similar for lime combined with 

 pectose. 



The phosphates, as appears from a careful microscopic exam- 

 ination of the ashes, are found principally in the contents of the 

 cells, and the easily soluble alkaline salts are diffused in the 

 liquid matter. If then it is the inorganic constituents especially 

 which modify the chemical action of plants, it must be in great 

 measure the pliosphates and alkalis, since this process takes place 

 principally in the inside of the cells and their contained juices. 



The flint and lime contained in the cells must have a constant 

 and direct proportion to the quantity of cells and the mass of the 

 whole plant ; the pliosphates and alkalis on the contrary rise or 

 fall with modifications of the chemical action. 



There are two circumstances especially in which wild vegeta- 

 tion is distinguished from that of our cultivated fields. 1st. In wild 

 plants the departing generation is again incorporated with the 

 ground. All the inorganic matters whicli they received from the 

 soil return to it, and in the most favourable form. In cultiAation, 

 on the contrary, great quantities of inorganic matter, and that 

 exclusively important for vegetation, are carried oflf with the 

 plants themselves, and in consequence the soil must in a short 

 time be exhausted if nothing be brought in in the shape of manure. 

 2ndly. Uncultivated ground becomes constantly richer in humus 

 through the decay of the plants which it produced, and the more 

 so because, in consequence of its never being disturbed, the 

 decomposition of the humus is indefinitely prolonged, while cul- 

 tivated land not only suffers from tlie removal of the crop, but 

 what liumus it contains is continually subject to decomposition 

 by the frequent exposure of a new surface to the atmosphere. 

 It may besides be mentioned that in cultivation, as the ground is 

 covered by a crop consisting of one plant only, the inorganic 

 materials are far less fully worked up than where the especial 

 exigencies of multitudes of plants of different natures are to be 

 supplied at one and the same instant. 



There is, however, one more important circumstance to be 

 mentioned before this part of the subject is closed, on which the 

 dependence of agricultural plants on their soil actually rests. The 

 geographical distribution of plants is determined by ^the con- 



