260 GANGRENE OF PLANTS. 



the whole leaf or branch rots off, or the shrub dies. 

 But the saaie kind of plant is often affected with a 

 much more serious disease, called by Thiery " la disso- 

 lution.'' This seems to be a sudden decay of the vital 

 principle, like that produced in animals by lightning 

 or strong electricity. In an hour's time, from some 

 unknown cause^ a joint, a whole branch, or sometimes 

 an entire plant of the Nopal, changes from apparent 

 health to a state of putrefaction or dissolution. One 

 minute its surface is verdant and shining; the next it 

 turns yellow, and all its brilliancy is gone. On cutting 

 into its substance, the inside is found to have lost all 

 cohesion, being quite rotten. The only remed}^ in this 

 case is speedy amputation below the diseased part. 

 Sometimes the force of the vital principle makes a 

 stand, as it were, against the encroaching disease, and 

 throws off the infected joint or branch. Such is the 

 account given by Thiery, which evinces a power in 

 vegetables precisely adequate to that of the animal 

 constitution, by which an injured or diseased part is, 

 by an effort of Nature, thrown off to preserve the rest. 



Nor need we travel to Mexico to find examples of 

 this. Every deciduous tree or shrub exhibits the very 

 same pheenomenon ; for the fall of their decaying 

 foliage in autumn, leaving the branches and young 

 buds vigorous and healthy, can be explained in no 

 other way. Yet Du Hamel laboured in vain to account 

 for the fall of the leaf* ; nor is it wonderful that he or 



* See his P/iys. dcs Arbrcs, v. 1. 127. 



