ELEMENTARY BOTANY. XXvii 



mately connected with the first formation of the new cell, As this cell increases in 

 size and its walls in thickness, the protoplasm and watery cell-sap become absorbed or 

 dried up, the firm cellulose wall alone remaining as a permanent fabric, either empty or 

 filled with various organized substances produced or secreted within it. 



192. The principal organized contents of cells are 



sap, the first product of the digestion of the food of plants ; it contains the ele- 

 ments of vegetable growth in a dissolved condition. 



sugar, of which there are two kinds, called cane-sugar and grape-sugar. It usually 

 exists dissolved in the sap. It is found abundantly in growing parts, in fruits, and in 

 germinating seeds. 



dextrine, or vegetable mucilage, a gummy substance, between mucilage and starch. 



starch or fecula, one of the most universal and conspicuous of cell-contents, and 

 often so abundant in farinaceous roots and seeds as to fill the cell-cavity. It consists 

 of minute grains called starch-granules, which vary in size and are marked with more 

 or less conspicuous concentric lines. The chemical constitution of starch is the same 

 as that of cellulose ; it is unaffected by cold water, but forms a jelly with boiling 

 water, and turns blue when tested by iodine. 



chlorophyll, very minute granules, containing nitrogen, and coloured green under 

 the action of sunlight. These granules are most abundant in the layers of cells imme- 

 diately below the surface or epidermis of leaves and young bark. The green colouring- 

 matter is soluble in alcohol, and may thus be removed from the granules. 



chromule, a name given to a similar colouring-matter when green. 



wax, oils, camphor, and resinous matter, are common in cells or in cavities in the 

 tissues between the cells, also various mineral substances, either in an amorphous state 

 or as microscopic crystals, when they are called Baphides. 



§ 2. Arrangement of the Elementary Tissues, or Structure of the Organs of Plants. 



193. Leaves, young stems, and branches, and most parts of phsenogamous plants, 

 ■*Bjg the first year of their existence consist anatomically of 



1, a cellular system, or continuous mass of cellular tissue, which is developed both 

 vertically as the stem or other parts increase in length, and horizontally or laterally as 

 Tl| ey increase in thickness or breadth. It surrounds or is intermixed with the fibro- 

 T ascular system, or it may exist alone in some parts of phsenogamous plants, as well 



8 ■ CI 7ptogamous ones. 



2, nfibro-vascular system, or continuous mass of woody and vascular tissue, which 

 > 8 gradually introduced vertically into, and serves to bind together, the cellular system. 

 « >a continued from the stem into the petioles and veins of the leaves, and into the 

 plant 6 and Pai tS ° f the flowers ' and is never whollv wanting in any phsenogamous 



tah fl' *? ^dermis, or outer skin, formed of one or more layers of flattened (horizon- 

 and J coherent, and usually empty cells, with either thin and transparent or thick 



Prot°^ qUe Walls- II covers almost all parts of plants exposed to the outward air, 

 aouflt •? their tissues from to immediate action, but is wanting in those parts of 



1Q4 #! ant8 which are constantly su! merged. 

 Sto t e P ider mis is frequently pierced by minute spaces between the cells, called 

 elast- i They are oval or mouth-shaped, bordered by lips, formed of two or more 

 a drt° T 8 ° dis P osed as to cause the stomate to open in a moist, and to close up in 

 oh? i 8te ° f the atmosphere. They communicate with intercellular cavities, and are 

 noon l J desi 8 ned t<> regulate evaporation and respiration. They are chiefly found 



IK 1^?' e8 P ecia % on the under surface. . t . 



anatn ■ , a P h amogamous plant has outlived the first season of its growth, the 

 and v C , 8truc ture of its stem or other perennial parts becomes more complicated 

 -En/ 617 dlfferen t in the two great classes of phsenogamous plants called UxogensanA 

 mTto" 3 ' Which correspond with very few exceptions to the two classes Dicotyledons 

 (Dio^ , n ^ COt y ledon8 d67), founded on the structure of the embryo. In Exogens 



•cotyledons) the woody system is placed in concentric layers between a central 



