BOOK II. 



PHYSIOLOGY ; OR, PLANTS CONSIDERED IN A STATE OF 

 ACTION. 



CHAPTER I. 



GENERAL CONSIDERATIONS. 



PLANTS have been thus far considered merely with reference 

 to their structure. Our next business is to inquire into the 

 nature of their vital actions, and to make ourselves acquainted 

 with what is known of the laws of vegetable life. 



In explaining these things, it will be useful, in the first 

 place, to give a summary exposition of the principal pheno- 

 mena of vegetation, and then to support the statement by a 

 detailed account of the more important proofs of all disputed 

 points. 



In this the student will be materially assisted by the 

 Physiologic Vegetale of De Candolle, a work of which it is 

 difficult to speak in terms of sufficient eulogy, but which may 

 be justly described as the most important production on the 

 subject of Vegetable Physiology, which, at the time of its 

 publication, had appeared since the Physique des Arbres of 

 Duhamel. 



I. If we place a seed (that of an apple, for instance) in 

 earth at the temperature of 32 Fahr., it will remain inactive 

 till it finally decays. But if it is placed in moist earth 

 some degrees above 32, and screened from the action of light, 

 its integument gradually imbibes moisture and swells ; the 

 tissue is softened, and acquires the capability of stretching ; 

 the water is decomposed, and a part of its oxygen, combining 



