ANALYTICAL CfLASS-BOOK OF BOTANY. 



the duct is the same — they serve to convey liquids. 

 Only the Spiral Ducts contain air. 



49. Pkosenchyma is the general name for all those 

 tissues which are composed of elongated cells with 

 pointed extremities, and is used to distinguish the 

 Pibro-oellular tissue from the Membranous-cellular tissue, 

 or parenchyma. It is the chief component of wood, to 

 which its greatly thickened tubes, running lengthwise 

 through the whole system, impart the high degree of 

 strength and toughness for which that substance is 

 remarkable. The mechanical basis of prosenohyma is 

 fibre. Thus the mechanical bases of all plants, and all 

 parts of the plant, are membrane and fibre; and the 

 chemical constituents of these are carbon, hydrogen and 

 oxygen. Out of these three elements, then, with a cer- 

 tain intermingling of earthy matter, by which a higher 

 degree of solidity is acquired, the vegetable fabric is 

 wholly constructed. These, with the addition of nitro- 

 gen, are termed the Universal Organic Constitdents 

 of Plants, because no organism can be constructed with- 

 out them. Nitrogen, as you have before learned (30), is 

 one of the elements of protoplasm, and is therefore a 

 vital agent ; but it is not deposited in the structure. 



50. The Vertical System. — The fibrous and tu- 

 bular cells run lengthwise, and this is the reason why 

 wood will not split across. The fibres themselves are 

 stronger than the substance that binds them together. 

 Such a disposition gives a tendency to longitudinal or 

 upright growth, and for this reason the system which 

 they compose is called the Vertical System. It is to 

 be distinguished from the Horizontal or Cellular System 

 by the direction of its growth, as well as by several 

 other features, which have already been mentioned, and 

 with which, in due season, you will be made familiar. 



51. Laticiferous Tissue. — This consists of irregular 

 branching tubes of considerable length, which seem to 

 have no definite connection with the other tissues. They 

 are abundant in such plants as have a milky juice, as the 

 Milk-weed, Celandine and Lettuce ; and for this reason 

 they are called the Vessels of the Latex, or Vessels of 

 the Milky Juice. These tubes are so very fine and trans- 

 parent, that they often elude observation, even with the 

 help of a powerful magnifier, and that especially when 

 they are young; but when old, and well gorged with 

 sap, they are easily seen. At fig. 14 they are represented 

 in a very highly magnified state. They are supposed to 



In what plants found? What forma of tho Duct convey liquids ?— what air! 

 Proscncliyma. Mechanical basis. Mechanical bases of all plants. Their 

 Chemical Constituents. What matter intermingled ? Universal Organic Con- 

 Btitnents. Of which is tho vegetable body constructed ? Which is the chief 

 agent in vital action » Direction of tubular cells. What system do they con- 



occupy the intercellular spaces, and their branches are 

 united by open mouths, so that there is a free communi- 

 cation throughout the whole system ; and in this respect 

 they may justly be compared with the veins of animals 

 The Vessels of the Latex abound in the inner bark, and 

 also in the leaf-stalk and under side of leaves. 



CHAPTEK V. 



CONTENTS OF THE CELLS. 



52. You have now obtained some idea of the elemen- 

 tary processes of vegetation, in the life, growth, multi- 

 plication and transformations of the cellular tissue. 

 You have been told how are produced from the primeval 

 sac, or simple roundish cell, all the vast varieties of 

 forms that distinguish the vegetable world, but you do 

 not comprehend this. You regard it still as a great 

 mystery, and even the language of the science has a 

 strange and mystical, not to say severe sound. Yet 

 with every step, as you advance, the views which you 

 obtain will be clearer, while the terms will be more easily 

 understood and remembered. And along with this, you 

 will unfold a continual pleasure in the discovery of new 

 truths, which might almost make the student wish to 

 unlearn his science, that he may have the joy of learning 

 it over again. 



53. Prom the few simple elements of sti-ueture and 

 vital action in plants (which, as you have learned, never 

 exceed four), an almost endless variety of combinations 

 is produced. Prom these four elements, carbon, hydro- 

 gen, oxygen and nitrogen, are formed substances as unlike 

 each other as possible ; such as starch, coloring matter, 

 acids, the bitter principle, and sugar. 



54. The Sap. — The liquids which are absorbed by 

 the roots, and pass upward through the stem, are the 

 crude sap. This is simply water holding certain sub- 

 stances in solution, and is therefore inorganic. On 

 reaching the leaves, by the peculiar action of the solar 

 light on their green coloring matter, an important chem- 

 ical action is introduced, and the character of the sap is 

 essentially changed. It is then a thickened whitish 

 liquid, known by the name of the Milk-sap, Elaborated 

 Sap, or Cambium. This liquid is the prepared material 

 of cell structure, and is therefore an organic substance. 

 It is carried to all parts of the system, and from it are 

 formed the whole vegetable fabric, and all which it contains. 



stitute? Laticiferous Tissue? What sometimes called? In what plants 

 found ? What parts of the plant ? 



General subject. Cheering views. Four vegetable elemoats— what com- 

 binations? Sap — Crude Sap— Elaborated Sap. 



