LECT. V.] THE ROOT. SOILS. 225 



closely set with fibrils. The reason of these cir- 

 cumstances is, that the root shooting out towards 

 the spots where the stimulus of nutriment is in 

 greater quantity, exhausts the little nourishment it 

 can obtain in adding to its length, and, therefore, 

 an insufficient supply is left for the stem and 

 leaves ; but in richer soils the whole of the fibrils 

 being surrounded by nutritious matter, a greater 

 quantity is actually taken up by a much smaller 

 surface of roots, and supplies more freely the her- 

 baceous parts of the plants. 



To ascertain the real nature of soils, chy- 

 mistry must lend its assistance ; and this mode 

 of examination is undoubtedly the most cer- 

 tain. Sir H. Davy has, however, justly re- 

 marked, " that the results of analyses consi- 

 " dered as affording indications of fertility must 

 " necessarily differ according to the variations of 

 " climate, situation, and other circumstances. 

 " Thus, the power of soils to absorb moisture 

 " ought to be greater in warm and dry countries 

 " than in cold and moist ones, and when the 

 " quantity of fine argillaceous earth they contain 

 " is larger. Soils likewise which are situated on 

 " declivities, ought to be more absorbent than 

 " those in the same climate situated on plains and 

 " valleys. The productiveness of soils must like- 

 " wise be influenced by the nature of the subsoil, 

 " or the earthy and stony strata on which they 



VOL. I. Q 



