l6'2 PHYSIOLOGICAL BOTANY. PART II. 



influences upon it, and by which it resists those mechan- 

 ical and chemical efforts which otherwise would soon 

 succeed in decomposing its substance. The existence 

 of such a property is equally evident in the vegetable as 

 in the animal kingdom. No one will deny that ve-. 

 getables live ; and we may perhaps believe, that the 

 general law of life by which they resist destruction, is 

 the very same in kind, however different it may be in 

 degree, as that by which animals are also maintained in 

 a state of existence. In animals indeed, the intensity 

 with which this vital property acts is greater than in 

 vegetables ; but, as a sort of compensation, we find that 

 vegetables are much more tenacious of life than animals. 

 A plant may be mutilated to a very great extent, and 

 its separate parts will still live, and are frequently ca- 

 pable of becoming distinct individuals ; and, although 

 there are certain creatures possessing a compound struc- 

 ture, among the lowest tribes of animals, yet even in 

 them this property does not reside in so eminent a 

 decree as in certain vegetables, every elementary organ 

 of which appears capable of existing in a detached 

 form, and of reproducing an individual, similar to the 

 original of which it formed a trifling and subordinate 

 part. This therefore, the " excitability" of life as it 

 has been termed, is a property which we may consider 

 common to both kingdoms of organised nature. 



(147.) Tenacity of Life. A plant may lose 

 nearly half its weight by drying, and yet be restored 

 by care. De Candolle has recorded an instance of a 

 Srinpervivum ccespitosum, which had been placed in a 

 herbarium for eighteen months, and from which he 

 afterwards detached a living bud and reared a plant. 

 But the tenacity of vegetable life is best exhibited 

 in the property which seeds possess, of retaining 

 their powers of germination after having been exposed 

 to very considerable extremes of heat and cold. Some 

 also, which have partially germinated, may be again 

 dried and kept for months, without losing the power of 

 germinating afresh, although they are sensibly weakened 



