EFFECTS OF PLANTS UPON THE SOIL. 95 



atmosphere a degree of nourishment suited to the increasing 

 wants of the plants ; the strength, fullness, and depth of 

 hue of the leaves and the stalks, particularly of the latter, 

 increase in proportion to the richness of the soil. 



This state continues till after the period of flowering, 

 when a change, worthy of note, takes place ; the roots dry 

 up, the stalks wither and change their color; and when 

 fructification is at length completed, both roots and stalks 

 have become mere skeletons, which answer but little pur- 

 pose either for nourishing animals or manuring earth. 

 During this period of vegetation what becomes of the 

 juices that were so abundant in the roots and stalks? 

 They have been consumed by the formation of the seeds. 

 It is undoubtedly the case that plants still continue during 

 fructification to absorb some portion of their nourishment 

 from the air and soil ; and this assists in the formation of 

 their seeds ; but by far the greatest share of the formation 

 of these is owing to the deposits contained in the organs of 

 the plants. 



The same holds true of perennial plants ; and it may be 

 observed, that when a tree produces fruit too abundantly it 

 becomes exhausted and dried, and bears only that which is 

 small and misshapen. The difference between annual and 

 perennial plants is, that the former die as soon as the process 

 of fructification is completed ; whilst the latter preserve 

 their leaves green and their roots fresh, for the purpose of 

 absorbing new portions of nourishment, to be deposited in 

 their vessels for food when the returning warmth of spring 

 shall cause them to require it. 



M. Matthieu de Dombasle, one of our most enlightened 

 agriculturists, has confirmed by experiments the doctrine 

 I have here advanced. On the 26th of June, 1820, at the 

 time of flowering, he selected, within a small space, forty 

 wheat plants of equal size and strength, each having three 

 stalks bearing heads ; he pulled twenty of the plants with 

 ail their roots, and left the rest to complete their fructifica- 

 tion. Having carefully freed from earth the roots of 

 those he had taken up, he cut the stalks two inches above 

 the base, and dried separately the roots, and the stalks 

 surmounted by their heads. 



The roots and the portion of the stalks remaining with 

 them weighed, grains 657 



The stalks, heads, and leaves, *' 1946.5 



Total 2603.5 



