2^6 GANGRENE OF PLANTS. 



ly " la dissolution.'' 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 some- 

 times an entire plant of the Nopal, changes from appar^ 

 ent 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 co- 

 hesion, being quite rotten. The only remedy in this 

 case is speedy amputation below the diseased part. 

 Sometimes the force of the vital principle makes a 

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

 throws off the infected joint or branch. Such is the ac- 

 count given by Thiery, which evinces a power in vege- 

 tables precisely adequate to that of the animal constitu- 

 tion, by which an injured or diseased part is, by an effort 

 of Nature, thrown oifto preserve the rest. 



Nor need we travel to Mexico to find examples of 

 this. Every deciduous tree or shrub exhibits the very 

 same phoenonienon ; for the fall of their decaying foli- 

 age 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 any body else, 

 who endeavours to explain the physiology of vegeta- 

 bles or of animals, according to one principle only, 

 whether it be mechanical or chemical, should entirely 

 iail. To consider the fall of leaves in autumn as a 

 ploughing, or casting off diseased and worn out parts^ 



* See his Phys. cies ,irbres, v. 1. 127. 



