146 



VEGETATION. 



604, Minute portion of a leaf of Viola tricolor, viewed 

 in perspective, showing, a, cells of epidermis above ; 

 b, compact parenchyma of the upper portion of the 

 leaf; c, loose parenchyma; d, epidermal-cells of the 

 lower surface with stomata, one cut and opening into 

 the intercellular passages. (Magnified 100 diameters.) 



735. THE STRUCTURE OF BRACTS, 

 sepals, petals, and other organs, 

 which are but modifications of 

 the leaf, hardly requires a separ- 

 ate notice. The same kinds of 

 vessels pervade their parenchyma, 

 but the spiral exist in a larger 

 proportion. In the pistil, the fibro- 

 vascular bundles may be traced 

 to the placenta, and thence into 

 the funiculua and raphe of the 

 ovule. In the more delicate or- 

 gans chlorophylle is wanting, and 

 the peculiar coloring, matter of 

 whatever other tint, is uniformly 

 diffused through the fluid con- 

 tents of the cells of parenchyma. 

 The depth of the tint depends on 

 the number of cells thus colored. 



CHAPTER V 



VEGETATION, OR THE PHYSIOLOGY OF PLANT LIFE. 



736. NEXT INQUIRIES. We have now briefly surveyed the mechan- 

 ism of the plant, both its outward forms and internal structure. We 

 next inquire into the uses of all this wonderful apparatus ; what the 

 specific office which each part performs in the economy of the plant ? 

 and how do all parts cooperate in the work of livingand growing ? 



737. THIS is A SUBJECT OF GREAT EXTENT, and involves many inquiries of deep 

 interest both in science and art, many inquiries, also, which have never been an- 

 swered. Our limits confine us to the bare statement of admitted principles, to the 

 exclusion of all speculative discussion. 



738. WHAT is LIFE ? This inquiry meets us at the beginning a 

 problem never solved. The spontaneous action of the plant, the self- 

 determined shapes which it assumes, we at once refer to this principle, 

 its vitality ; but of the nature of this principle itself we can only say, 

 Is it not a direct emanation from the Supreme Will, the Fountain of 

 all life ? 



739. VEGETATION is DOUBTLESS THE LOWEST FORM OF LIFE. It 

 springs directly from inorganic or mineral matter, and is the first step 

 in the organization of mineral matter. Its material is, therefore, min- 

 eral matter rendered organic through the vital force. 



