FALL OF LEAVES. 45 



of visiters. The humble plant, Mimosa pudica, possesses 

 similar properties. 



The irritability of plants is also shown, by the fact, that 

 poisons operate on them in the same manner that they do on 

 animals. A weak solution of corrosive sublimate, or of ar- 

 senic, kills plants, by bringing on a kind of inflammation, or if 

 made stronger, destroys them directly by corrosion. These 

 poisons operate in the same manner on the animal system. 

 Vegetable poisons, such as prussic acid, kill plants by 

 destroying their irritability, and on animals this fluid produces 

 precisely the same effect. 



Fall of the Leaf. The fall of the leaf appears to be inti- 

 mately connected with the irritability of the plant. This takes 

 place in some plants earlier in the season than in others. In 

 general, perennial plants, or trees, begin to drop their leaves 

 about the middle of autumn. This is preceded by a change 

 of color, indicating that their vegetating powers have become 

 exhausted, arid that their irritability, or vital energies, have 

 ceased to act, at least for the season. This process is rapidly 

 increased by the accession of frost, which in a single night, 

 by stopping entirely the motion of the sap into these organs, 

 often leaves them perfectly dead in their places, and by the 

 morning breeze, the tree is totally stripped of its foliage. 



The different colors which the different species of forest 

 trees assume at this season, afford to the eye one of the most 

 " splendid objects of an autumnal landscape," while to the 

 mind of a rational being, it ought to become the subject of 

 deep and profitable contemplation. The change which the 

 leaf undergoes, and its "fall" is but an illustration of the 

 state of all mortal beings, and a type of their final descent to 

 the grave. Disease, or old age, will as certainly exhaust the 

 vital powers, and destroy the irritability of man, as the autumn, 

 and the frost, do that of the leaf, and like it, we must all 

 sooner or later, fall to the ground, and " return dust to dust." 



Duration of Leaves. In general, trees which put forth 

 their leaves earliest in the spring, begin to lose them earliest 

 in the fall, though this is not universally the case. Evergreen 

 trees, such as Laurel (Kalmia,) and Rosebay, (Rhododendron,) 

 do not let fall their leaves during the usual season, but 



In wtat manner do poisons operate on plants ? How is the fall of the 

 leaf connected with the irritability of plants ? Is there any proportion 

 between the time in which trees put forth their leaves in the spring, and 

 lose them in the fall ? 



