Dr Davy's Agricultural Discourse. 297 



the sea fowl, the source of guano ; and, in consequence, even 

 when insects are destructive they may fertilize, so that some- 

 times it may be a problem whether the good effected by them 

 in one way may not preponderate over the evil they occasion 

 in the other. But it is not my wish to appear paradoxical ; 

 I mention these circumstances because I believe them to be 

 deserving of attention, and fit to illustrate the nature of ani- 

 mal manures. 



^dly^ Of the fertilizing means derived from vegetable mat- 

 ter. That vegetable matter should be fit to be the food 

 of plants, is most easy to conceive a priori; and that it is fit, 

 is proved by the most extensive experience, and this, gene- 

 rally, and without exception, in different degrees, as in the 

 instance of animal matter ; and, also, as in the instance of 

 animal matter v*^hen undergoing decomposition, — that is, 

 when under the influence of moisture and atmospheric air, 

 the vegetable matter is becoming resolved into the com- 

 pounds from whence it originated. It is a happy circum- 

 stance for agriculture, that vegetable matter in a dry state 

 undergoes little or no change on the surface of the soil ; it 

 also is a happy circumstance, that it undergoes little or no 

 change under the soil, even when moist, if atmospheric air 

 be excluded. Moisture and atmospheric air are essential to 

 the growth of plants ; and, being essential also to the de- 

 composition of vegetable matter, the latter takes place when 

 it can be useful to the former. One of the peculiarities of 

 cane cultivation in Barbadoes, and, I apprehend, a very judi- 

 cious one, is the strewing of the leaves of the last crop on 

 the surface of the cane-field to protect the young plants from 

 the sun's rays and from parching winds. Conjoined with 

 this effect, is another which takes place, though I believe not 

 contemplated, viz., that of manuring the young canes. So 

 long as drouglit prevails, the old leaves are protectors, them- 

 selves unchanged ; so soon as the rains set in, even if there 

 be only a single shower, their decomposition commences, and 

 their fertilizing influence is exerted. 



An idea commonly prevails, that soils by long culture are 

 worn out and exhausted. Under one system of cultivation 



VOL. XLIII. NO. LXXXVI. — OCTOBER 1847. U 



