80 Horticultural Chemistry. 



Parts 



-g Burnt clay' - - - - - 29 



g^ The richest soil (in one hour) - _ _ 23* 



o \ Coal-ashes - - - - - 14 



o I Lime (part carbonate) - - - - 1 1 



'~' I Crushed rock salt - - - - 10 



I Gypsum - - - - - 9 



l^Chalk - - - . . 4 



The absorbing power of a manure is much influenced by 

 the state in which it is presented to the atmosphere. In a 

 finely divided state, mei'e capillary attraction assists it; hence, 

 as we have before insisted, the importance of keeping the soil 

 frequently stiri'ed, by hoeing, &c. The most aincient Roman 

 agriculturists were aware of this. " What is good tillage ?" 

 says Cato, in his De Re Riistica. " To plough. What is the 

 second thing? To plough. The third is to manure." But a 

 mere mass of cotton, by means of capillary attraction, will 

 absorb moisture from the air, yet it parts with it at a very 

 slight elevation of temperature ; it is of importance, therefore, 

 to ascertain which are the manures that not only absorb but 

 retain moisture powerfully. The following results of my 

 experiments throw some light on this point : — 



Minutes 

 Pig clung, evaporated to dryness, at a temperature of 106°, 

 and then moistened with 6 parts of water, required for 



being reduced to dryness again, at the above temperature 135 

 Horse dung, under similar circumstances - - 90 

 Common salt - - - - 75 

 Soot ... - - 75 

 Rich soil - - - - - 52 

 Chalk - - . . _ 29 

 Poor soil (siliceous) - ... - 25 

 Gypsum - . - - - - 18 



These experiments point out a criterion by which we easily 

 ascertain the comparative richness of any two given soils or 

 manures ; the most fertile will be the most absorbent and re- 

 tentive. 



Some manures increase the growth and vigour of plants, 

 by stimulating their absorbent and assimilating organs. 

 This will only be admitted by those, who, like myself^ al- 

 low that plants are gifted with sensation; space cannot be 

 permitted me to argue as I would to those who dissent 

 from this opinion, but a few facts, as enumerated in my 

 Outlines of Botany (Gard. Mag., Vol. II. p. 338.), will, I 

 think, demonstrate that it is impossible to deny that they 

 possess some degree of sensation. " The Venus's Fly Trap 

 (Dion^^^a muscipula) has jointed leaves, which are furnished 



* Sir H. Davy. 





