SECT, I. EXCITABILITY. 



in the spring and autumn, than in either the sum- 

 mer or winter ; as may readily be seen by watching 

 the progress of the growth of the annual shoot, 

 which after having been rapidly protruded in the 

 spring, remains for a while stationary during the 

 great heat of summer, but is again elongated during 

 the more moderate temperature of autumn. 



There are also several substances which have been 

 found to operate as stimulants to the agency of the 

 vital principle when artificially, dissolved in water 

 and applied to the root or branch. The germination 

 of Peas is accelerated by means of moistening them 

 in water impregnated with oxygenated muriatic 

 acid, as was first ascertained by Humboldt: and 

 the vegetation of the bulbs of the Hyacinth and 

 Narcissus is accelerated by means of the application 

 of a solution of nitre. * Dr. Barton, of Philadelphia, 

 found that a decaying branch of Liriodendron tu- 

 lipifera and a faded flower of the yellow Iris re- 

 covered and continued long fresh when put into 

 water impregnated with camphor ; though flowers 

 and branches, in all respects similar, did not recover 

 when put into common water. 



* Willdenow, p. 295. 



