514 Retrospective Criticism. 



of years to produce blossoms. Sometimes blossoms are produced, which, from 

 defect, or want of vigour, prove abortive ; and when this is the case, by re- 

 moving from the plant all the blossom-buds before they expand, for one or 

 more years in succession, more vigorous blossoms will be produced, and the 

 production of fruit insured. This is the reason why on fruit trees a defective 

 crop is generally succeeded by an abundant one, and the contrary; and why 

 double-blossomed trees or herbs, which yield no fruit, produce abundance of 

 blossoms every year." 



It has been 4 customary to call the cause of fruiting an accumulation of 

 nutritive matter. Were this the case, we would add to the fruitfulness 

 of a tree by augmenting the quantity of its food or nutritive matter. The 

 reverse of this, however, more often takes place, as in ringing and taking 

 away roots, impoverishing the soil, &c, all which diminish the quantity of 

 nutritive matter, and yet generally add to fruitfulness. It is not that impove- 

 rishing is itself the cause : were we able to increase the light and heat as we 

 can increase food, there would be less cause for impoverishing. The supply 

 of food, however, is most at our command ; the others, especially the light 

 (the most needful), we have but little power over, and must, therefore, curtail 

 the food to suit our limited means. A certain highly elaborated state of the 

 food is necessary before fruit-buds can be formed : experience teaches us this, 

 as we see that fruit-buds are always most plentifully formed in seasons 

 when the accumulation of the chemical power of the light from an unclouded 

 sky has added most to the power of the leaves. Chemistry has not yet been 

 able to unravel the changes required to bring the sap into a proper condition 

 for producing fruit-buds ; but that it is the quality, more than the quantity, 

 experience abundantly points out. 



" 157. Magnesia, for all practical purposes, may be considered as lime ; it 

 is not very common in soils, and, though it is said to be inimical to vegetation 

 under some circumstances, yet this appears very doubtful." 



Magnesia, in its caustic state, is much longer in returning to the mild state, 

 by regaining its carbonic acid from the air, than lime, especially if lime is 

 present, as it generally is with magnesia. In this caustic state, it may be 

 dangerous in excess ; but, being more sparingly soluble than caustic lime, 

 excess is not so apt to occur. 



" 158. The iron of soils is mostly found in a state of rust, or oxide. There 

 is scarcely any soil without it ; but it is never very abundant in soils naturally 

 fertile. In a dry state the oxide of iron is insoluble in water, and not injurious 

 to vegetation ; but, when in consequence of saline substances in the soil, or 

 applied to it, a salt of iron is produced, the iron becomes soluble in water, 

 is taken up by the roots of plants, and is very injurious to them. Iron in this 

 state is termed hydrate, and its evil effects are to be counteracted by caustic 

 lime, with which it forms an insoluble compound." 



The sulphate of iron, being the most soluble of any of the salts of iron, is 

 most hurtful. Turning up the soil, and exposure to the air, change the 

 sulphate into an insoluble peroxide; and quicklime decomposes the sulphate, 

 so will also mild lime or chalk, but not so powerfully, the sulphuric acid of 

 the iron replacing the carbonic of the lime. 



" 188. Hair, wool, feathers, leather, horn, rags, &c, decompose much more 

 slowly than excrementitious or vegetable manures ; but they are exceedingly 

 rich in gelatine and albumen, and are therefore very desirable where the 

 object is duration of effect, as well as luxuriance. Dead animals of every 

 kind, including fish, make excellent manure ; and when there is any danger 

 anticipated from the effluvia which arises during decomposition, it is readily 

 prevented by covering or mixing the putrid mass with quicklime. In this 

 way, nightsoil and the refuse of the slaughter-houses in Paris, Lyons, and 

 other Continental towns, are not only disinfected, but dried under the name 

 of poudretle, and compressed in cakes, so as to form an article of commerce. 

 Sugar -bakers' scum, which is obtained from sugar refineries, consists of the 

 blood of cattle and lime ; it can be sent, in a dried and compressed state, 



