140 



Effect of saline 



IRRITABILITY OF VEGETABLES. 



impregnations *h e j r roots, 

 ni the irrita- 

 bility: 



and of oxirnu- 



mtic 



and other 

 gasses. 



Oxigen dees 

 not act a i a 

 stimulus to 



vegetables. 



I put some small lettuce plants, while. in flower, with 

 to vegetate in water, to which wa9 added in 

 some of the vessels a small portion of muriate of soda, in 

 others of nitrate of potash, and kept them thus in the open 

 air some days. If any portion of these salts were absorbed 

 from the water, they did not appear to increase the irrita- 

 bility of the plants, for the exudation diminished in quantity. 



J mixed acids also in water, in such proportion as to be 

 barely sensible to the taste, and particularly nitric and 

 oximuriatic acid in various proportions, and then placed 

 several small plants of lettuce in full flower in the vessels, 

 with similar effect. If a larger quantity of acid were added 

 to the water, it appeared to injure the plants, and their 

 irritability likewise decreased more quickly. 



I applied this kind of stimulus to the surface of plants, 

 to see if it would act externally. On immersing a branch 

 of lettuce in ajar filled with oximuriatic acid gas, and 

 taking it out in a few seconds, it exhibited the usual 

 exudation when stimulated: but when it was kept longer 

 in the gas, it was evidently injured, and its irritability 

 greatly decreased. Nitrous and sulphureous vapours were 

 still more injurious. 



It appears then that these stimuli, which are so much 

 vaunted as inceasing the irritability of animals, are not 

 appropriate to the irritability of vegetables*. 



* Those f;icts, that are admitted as proofs of the stimulant action 

 of certain substances or principles in the vegetable economy, do not 

 appear to me decisive. 



It is generally supposed, that oxigen is a powerful stimulus to 

 vegetables, because it has been observed to accelerate the germi- 

 nation of seeds- this effect being ascribed to its stimulating their 

 vascular system, and rendering their circulation more active. But 

 as it appca:s from the observations of Mr. de Saussure the younger, 

 that the oxigen entering into germination is neither absorbed nar 

 assimilated in this process, but employed in forming carbonic acid, 

 . I conceive it does not act as a stimulus, but merely serves to carry 

 off from the germinating seed the carbon; an element which, as is 

 shown in some of my observations respecting the action of light on 

 germinating seeds, inserted in the Ojmscoli scelti of Milan, seems 

 injurious to the developement of the embryo; and of which nature 

 seems at that time disposed to free herself, as noxious or superfluous. 

 This appears to be' the reason why oxigen accelerates germination. 



I immersed 



