STRUCTURE OF PLANTS. 



A perfect plant consists of the root, the stem or trunk, 

 the stalk, the leaves, the flower, and the fruit. 



Roots are either annual, lasting one year, as the Poppy, 

 Barley, &c. ; biennial, when produced in one year, and 

 flowering the next, as Wheat, Canterbury Bell, &c. ; or 

 perennial, when they last many years, as the Rose, Trees, 

 &c. There are various kinds of roots, some are bulbous, 

 as the Tulip and Onion ; tuberose, as the Potatoe and 

 Turnip ; fusiform, as the Carrot and Radish ; orjibrous, as 

 in Trees and Grasses. The root generally consists of two 

 parts ; the body and the fibres : the latter is the part 

 which imbibes nourishment from the earth for the support 

 of the plant. The seed of a plant committed to the ground, 

 swells by the moisture it imbibes, and, in a few days, 

 throws out two shoots ; the first strikes downward into 

 the soil, and forms the root or radical ; and the other forces 

 its way into the air. As soon as the young plant feeds 

 from the soil, it requires the assistance of leaves, which 

 are the organs by which the plant throws off its super- 

 abundant fluid. Vegetation is then essentially injured by 

 destroying the leaves of a plant. It not only diminishes 

 the transpiration, but also the absorption by the roots ; 

 for the quantity of sap absorbed is always in proportion to 

 the quantity of fluid thrown off by transpiration. 



The Trunk, or Stem, is that part of a plant which pro- 

 duces the leaves and flowers, and serves to elevate them 

 above the ground. It consists, 1. Of the Epidermis, cuticle, 

 or exterior thin membranous covering, furnished with 

 pores, which transmit or throw off the excretory products 

 of vegetation; answering to the skin of animals. 2. The 

 Cor (ex, or outer bark, consists of vesicles and utricles, (small 

 membranous cavities or cells to receive the sap,) so very 

 numerous, and close together, as to form a continued coat- 

 ing. It is among these glands that the work of digestion 

 appears to be performed ; and the product of this elabora- 

 tion is after waids conveyed through the whole vegetable, 

 by vessels propagated through all its parts ; these conduits 

 even passing through the body of the tree, crossing the 

 ligneous strata. In this net-work it is that the colouring 

 matter of vegetables is decomposed : the light which 

 penetrates the Epidermis concurs in enlivening the colour : 



here, likewise, it is that oils and resins are formed, by 

 the decomposition of water and the carbonic acid. 3. The 

 Liber, or inner bark, is the part in which the vital principle 

 of a plant is chiefly seated ; its parts are easily detached 

 from each other ; their laminae, (fibrous scales or layers,) 

 are not extended lengthwise along the stem, but are curved 

 in various directions ; and leave openings, or meshes be- 

 tween them, which are filled by the cellular matter itself, 

 and it is from their resemblance to the leaves of a book, that 

 they have been called liber. It is this part of the bark on 

 which the ancients wrote, before the invention of parch- 

 ment, or paper. In proportion as these coatings approach 

 the ligneous body, or wood, they become hard ; and at 

 length form the external softer part of the wood, which 

 workmen call the sap. The wood or ligneous part of the 

 plant, is a compact fibrous substance, formed by new 

 layers, which are added, every year, from the innermost 

 part of the bark ; so that the age of a tree, or shrub, may 

 be ascertained by the number of ligneous circles which 

 appear upon cutting the stem near the root. 



The bark is the most essential part of the vegetable, by 

 means of which the principal functions of life, such as 

 nutrition, digesting the secretions, &c. are performed. 



The bark of a tree is only a congeries of the roots of the 

 individual buds of the plant. These roots spread them- 

 selves over the last year's bark, making a new bark over 

 the old one, and thence descending, cover with a new 

 bark the old roots also. 



The wood, or ligneous part, is not essential, many plants 

 being without it ; such as grasses, reeds, and all plants 

 that are hollow within. 



The hollow Oak-trees, and Willows, are often seen with 

 the whole wood decayed and gone, and yet the few re- 

 maining branches flourish with vigour. 



Grasses, properly speaking, have only the cortical part. 

 The thin outside cover of the bark is of great consequence 

 to them : it is of great strength, and appears to be con- 

 stituted of a sort of glassy net-work, which is chiefly 

 siliceous earth, as has been lately ascertained. This is 

 the case in the Wheat, Oat, and in different plants. 



The Stalks are those parts which branch out from the 



