EXTRACTS FOREIGN AND DOMESTIC. 335 



tity of the organic principles of that fluid (sulphuro-nitrogenous 



I compounds). ° 



j One of the plants will exhaust the ground of these principles, 

 whilst with the same conditions of culture for the other, which 

 has removed from it a smaller quantity of phosphates, it will still 

 remain fertile for a third kind of plant. 



This is, therefore, the reason why with the development of cer- 

 tain parts of plants which, such as the seeds, much exceed all the 

 others in their richness in the organic principles of the blood, the 

 soil loses much more of the phosphates, and is exhausted much 

 more than by the culture of herbaceous plants, or of tubercles and 

 roots which contain very little of them in proportion 



Besides, it is clear that if two plants which require in equal 

 times the same quantity of the same principles, grow side by side 

 3n the same ground, they will partake the principles of the latter. 

 Ihat which one of them introduces into its organism, the other 

 :»nnot appropriate. 



If the soif on a limited space (surface and depth) contain not 

 nore of these inorganic aliments than ten plants require for their 

 pomplete development, twenty of the same plants cultivated on 

 he same surface will attain only half their development: the 

 Immber of their leaves, the strength of their stems, and the num- 

 )er ot seeds should present a difference. 



Two plants of the same nature should be reciprocally injured, if 

 .rrown within a certain distance they find in the ground or in the 

 iitmosphere which surrounds them a less quantity of the aliments 

 ijrhich are necessary for them, than they require for their complete 

 ievelopment. There is no plant more injurious in this manner to 



II plant of wheat than a second plant of wheat, or to a potatoe 

 )lant than another potatoe plant. We find, indeed, that cultivated 

 )lants greatly excel at the border of the fields, in strength and in 

 lumber of seeds and tubercles, those which grow in the middle. 



Hut the same case should be reproduced, in a perfectly similar 

 Qanner, if we cultivate the same plant no longer by the side of 

 he other, but one after the other during several years on the same 

 oil. Let us admit that the soil contains a quantity of silicates 

 nd phosphates sufficient for 1,000 crops of wheat, it will be sterile 

 f the same kinds of plants after 1,000 years. Let us represent 

 |he surface of this field as exhausted to the bottom which nourishes 

 he roots of the plants of the first crops ; let us replace the bot- 

 om by the surface, and the surface by the bottom, and we then 

 ■ave a new surface, which, being much less exhausted, again en- 

 ures us a series of crops : but this state of fertility also has 

 imits. '' 



, The less rich the soil is in these mineral aliments, so indispensa- 

 tle to plants, the sooner will the period of exhaustion arrive • but 

 - is clear that we restore it to its primitive state of fertility by 



