CHAPTER III. 



GROWTH AND SECRETIONS. 

 47. 



^ I ^HE progress of the growth of a plant, and 

 -- the annual course of vegetation remain to 

 be considered, but it must be borne in mind, to 

 use the words of Professor Henslow, that " of 

 the precise manner in which the assimilation of 

 nutriment takes place we know nothing, and the 

 first steps towards the formation and develop- 

 ment of any organized being are entirely con- 

 cealed from us." New cells, fibres, and vessels 

 are most undoubtedly formed, or the leaf buds 

 must remain for ever undeveloped, but we are 

 ignorant of the immediate cause, and of the first 

 commencement of the effect ; for when we say 

 that the vital action is excited (whether in the 

 growth and nourishment of a plant or an ani- 

 mal,) what do we more than state a fact, whose 

 course we may indeed follow when we have 

 once observed it, but whose origin is, in the 

 present state of our knowledge, beyond our 



