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Outlines of Horticultural Chemistry : 



vessel c, which has a small hole and plug at g, for the purpose 

 of filling it with water ; and a small pipe d, for the escape of 

 the steam when the water is brought to a boiling temperature ; 

 h is a small pair of grain 

 scales. To ascertain the mois- 

 ture retentive power of a soil, 

 put 10 grains of it, previous- 

 ly dried by exposure to a 

 temperature of 212° (the 

 boiling point of water), for 

 half an hour, by having it 

 laid upon c, Avhilst the water 

 within it is kept boiling for 

 that period. On the J grs. of 



previously dried soil put, by means of a small quill, three drops 

 of clean water ; ascertain the exact weight of these, usually 

 4 grains ; then suspend the beam, so that the pan of the scales 

 containing the soil may rest upon c, as represented in the 

 sketch, the weight of the water having previously been re- 

 moved from the other scale-pan f. The water in c must be 

 kept boiling, and the exact number of minutes noted that is 

 required to evaporate the added moisture, so as to return the 

 beam into equilibrium. It was by means of this apparatus that 

 I obtained the comparative results detailed in a former volume. 

 I have always found those soils proportionably unproductive, 

 the first from containing too much alumina, and the second 

 from a redundancy of silica, as they required more than 50 

 minutes, and less than 25 minutes,, to deprive them of half their 

 weight of moisture. 



I shall now proceed to consider some of the diseases of 

 plants, whose ravages affect the horticulturist, and on which 

 science may afford some light. Plants being organised bodies, 

 whose parts, in the common course of nature, are subject to 

 waste and decay, the functions of these are consequently liable 

 to disarrangement, and such disarrangement constitutes dis- 

 ease. Such morbid affections are not, however, always the 

 consequences of old age : they are often caused by matters 

 being absorbed from the soil which are mimical to the consti- 

 tution of the plant ; from a want of those that are beneficial, 

 as well as from their excess ; from violent and sudden transi- 

 tions of temperature ; from wounds, and from the attacks of 

 vermin. " Animals," said the late Dr. Good, " are liable, as 

 we all know, to a great variety of diseases ; so, too, are vege- 

 tables, to diseases as numerous, as varied, and as fatal ; to 

 diseases epidemic, endemic, sporadic ; to scabies, pernio, ulcer, 

 gangrene ; to polysarcia, atrophy, and invermination. What- 



