STIMULATING MANURES. 75 



to be solved, and of which the solution cannot be found 

 in the stimulating properties of the plaster. 



Hitherto it has been sufficient to state the good effects 

 of plaster, in order that agriculture might be enriched by 

 so important a discovery. The fact alone is sufficient for 

 the farmer, and it is not the only one in which the theory 

 can add nothing to the practice. I shall, however, give 

 here a few of my ideas upon the action of plaster ; and 

 I publish them with the more confidence, because they 

 appear to me to be deduced from well-established anal- 

 ogies. 



It is proved, that those salts which have a base of lime 

 or alkali are the most abundant in plants. Analysis also 

 shows that the different salts do not exist in the same pro- 

 portions, either in plants of different kinds, or in the dif- 

 ferent parts of the same plant. 



On the other hand, observation shows us every day, 

 that these substances, to be beneficial to plants, must be 

 presented to them in proper proportions ; for if too great 

 a quantity of salts easily soluble in water be mixed with 

 the soil, the plants will wither and die ; though they will 

 languish, if totally deprived of the salts. A little marine 

 salt, mixed with dung and spread upon the soil, excitee 

 the organs of plants and promotes vegetation ; but too 

 much will produce a pernicious effect upon them. 



If we now consider that salts can act upon plants, only 

 in proportion to their solubility in water, through which 

 medium they are conveyed, we can conceive, that those 

 which are least soluble will be productive of the greatest 

 advantage. 



Water can hold in solution at any one time but a small 

 portion of these saline substances ; and as they will al- 

 ways be conveyed into plants in the same proportions, 

 their effect will be equal and constant, and will be con- 

 tinued till the soil be exhausted of the salts. The length 

 of this period will be according to the quantity of them 

 which is contained in the sojl, and to the plants not being 

 rendered liable to receiving more of them than it needs. 



The solubility of plaster in water appears to be pre- 

 cisely of the degree most beneficial ; 300 parts of water 

 will dissolve only 1 of plaster. Its action is therefore 

 constant and uniform, without being hurtful. The organs 

 of plants are excited by it without .being irritated and cor- 

 roded, as they are by those salts which, being more soluble 



