FOOD OF PLANTS IN GENERAL. 479 



Hj 



examining their own data for regarding the organic constituents of plants 

 as a principal source of their nourishment.* 



Boussingault has performed an interesting experiment on a small 

 scale. He sowed 1-072 mgr. of peas in a mixture of burnt clay and 

 sand, and watered it with distilled water; the ripe plants yielded 4-441 

 mgr., thus making 4' 14 times as much as was sown. According to 

 Block, when 138 Ibs. are sown on an acre, in the third year of the 

 manuring 880 Ibs. are harvested. In burnt clay or sand the harvest 

 would have been 571 '32 Ibs., according to the result of the experiment 

 by Boussingault, the difference showing how much organic substance is 

 necessary for the healthy development of the peas. The same experi- 

 ment has been tried on a large scale, with far more splendid results, for 

 many centuries in Cuba, and for 60 years in France. The Tierra colo- 

 rada, in the higher regions of the island of Cuba, produce from year 

 to year the richest harvests of Coffee and Indigo. This soil is never 

 manured, and is a pure clay, which in other places would be called an 

 iron soil. A very accurate analysis of this earth, in the Laboratory of 

 the Agricultural Institute of Jena, by Herr Wapler, gave the following 

 results : 



The earth is very fine, and contains only a small quantity of insoluble 

 quartz, and small bits of chalk or limestone. It is soft to the feel, and of 

 a dark brown colour. 



A. Soluble in Hydrochloric acid .... 24'0 

 Oxide of iron . . . 12-20 

 Alumina .... 6-00 



Carbonate of lime . . 5-80 



Magnesia .... traces 



24-00 



B. Insoluble in Hydrochloric acid . . . . 75-4 



a. Humic acid, soluble in ammonia 



traces 



b. In Sulphuric acid, soluble in 



potassa . . . . 1*41 



Alumina, with traces of oxide of 



iron .... 34-34 

 Magnesia .... 0*71 



c. Silica .... 38-94 



75-4 



C. Loss 0-6 



100-00 



In France the following experiments have been made between the 

 mouths of the Gironde and the Adour. The sand-downs which are 

 washed from the sea are carried by the west wind into the interior, 

 and thus large districts of the land are converted into a kind of 



* Thus, according to the calculations of Block (Mittheilungen landwirthschaftliche 

 Erfahrungen und Grundsatze, vols. i. and iii.), a good wheat soil will yield annually 

 2075 Ibs. per acre of dry matter, and receives 1167 Ibs. of dry manure; but the manure 

 contains, on an average, 30 per cent, of ashes, whilst the cultivated plants contain but 

 5 per cent., so that the proportions of organic substances are as 794 to 1971. 



