CONTENTS OF THE CELLS. 



9 



55 Classification ov Pkoducts. — The peculiar 

 secretiuns of plants are of two kinds — those which are 

 composed of the elements of pure cellulose, or of carhon, 

 hydrogen and oxygen, as Sugar, Starch, Acids and Oils, 

 and those in which nitrogen is combined with the other 

 three elements, as Gluten, Albumen, and the Alkaloids. 

 The first are called Ternary Products, because they 

 have but three elements, and the second Quaternary 

 Products, because they have four. 



TERNARY PRODUCTS. 



56. Starch. — This is not only one of the most im- 

 portant, but also one of the most interesting and remark- 

 able of vegetable secretions. It is a highly organized 

 substance, as may be seen by referring to fig. 1, Plate II. 

 which shows two well-defined starch-cells. At 6 are two 

 distinct grains separated from the cell. Each of these 

 grains consists of numerous layers deposited round a 

 nucleus; but as the layers are of unequal thickness, 

 the nucleus is not in the middle. Starch is found in 

 every plant and every part of the plant ; but it abounds 

 in tubers, roots, seeds, and in the pith of the Sago Palms. 

 It is an important principle of nutriment, useful in the 

 Arts, and under the microscope exhibits the most inter- 

 esting and elegant forms. A good test of the presence of 

 starch is that it turns deep blue or violet, when moistened 

 with a solution of iodine. 



57. Dextrine. — This is a form of starch soluble in 

 cold water. It has not only the same elements as pure 

 cellulose, but they are combined in precisely the same 

 proportions. In the course of growth, when there is an 

 excess in the supply of dextrine, it is solidified, and in 

 the form of starch is accumulated for future support. 

 When its active presence is again called for, it is recon- 

 verted into dextrine, and being thus rendered soluble in 

 cold water, it enters readily into the vital -operations. 



58. Sugar. — This product, in the living plant, gener- 

 ally exists in solution, though it sometimes occurs in the 

 nectaries in the form of crystals. It is abundant in all 

 the growing parts, in pulpy fruits, sweet roots, and in 

 the sap of the Kock-Maple and Sugar-Cane. Sugar, 

 starch and dextrine are nearly identical; and in the 

 vital action of plants they are repeatedly converted and 

 reconverted into each other. 



59. Mucilage or Vegetable Jelly has very 

 nearly the same composition as starch. When dry it is 



Peculiar Becretions. Those wlilcli are composed of tlie elements of cellulose. 

 What called'? Why ? Those in which nitrogen is comhined. What called ? 

 Why? Starch, in what plants found ? What parts! Uses. Test of starch. 

 Dextrine, difference between it and starch. What changes occur ? Sugar, in 

 what state? What plants? What parts found? What snhstances nearly 



tough and horny, but it swells and becomes gelatinous by 

 the application of moisture. It is not only contained iti 

 the cells, but, in some instances, it forms a large portior, 

 of the cell wall, as in some of the Sea-weeds. In thai 

 species which is known as Carragheen Moss, the cell 

 wall — and, in fact, the entire substance of the plant — w 

 composed of mucilage, and to this it is indebted for its 

 culinary celebrity, being much used in the preparation of 

 blancmange. Mucilage is soluble in cold water, and is 

 found in the tubers of the Orchis, the bark of Slippery 

 Elm, the leaves of the Sassafras tree, the seed of Flax, 

 and in the bark, roots and seeds of many other plants. 

 It also appears as an excretion in Gum TragacantL 



60. Essential Oils. — These are generally volatile 

 and aromatic, and thus they give to plants their peculiar 

 odors. They are well known in their concentrated forms, 

 which, in the hands of the druggist, are converted into 

 essences, to be used in Medicine and Perfumery, as the 

 Oil of Peppermint and the Oil of Orange -flowers. 

 What is commonly known as the Spirits of Turpentine is 

 an essential oil obtained by distillation from Turpentine 

 — a resinous substance that exudes from Pines and other 

 Cone-bearing trees. 



61. All these substances undergo various changes on 

 exposure to the air, by which they are converted into 

 Kesins, Gums, Wax and Balsams. Having no properties 

 which can either nourish the plant or be instrumental in 

 its growth, they may safely be considered as excretions. 

 The Leaf is the only excreting organ of vegetables, and 

 through this only liquids or gases can be exhaled. Sub- 

 stances, therefore, which are inclined to pass into the 

 solid state must generally be retained in the system, but 

 sometimes they exude directly from the surface in the 

 form of Gums, Resins, and like substances; but they 

 chiefly pass into the superannuated tissues, seeming 

 especially inclined to occupy the intercellular spaces. 

 The essential oils abound in flowers and leaves of herbs 

 and shrubs, and the bark and fruits of aromatic trees. 



62. Caoutchouc. — This substance belongs to the 

 same class as the next above, and like them may be 

 termed an excretion, as it seems to have no part or ofiice 

 in the vegetable life and growth. It occurs in the 

 form of minute globules, which are suspended in the 

 milky juice of many plants in precisely the same manner 

 as the globules of butter in animal milk. When the 

 liquid is left undisturbed, the globules, being lighter, 



identical? Mucilage, what resemble? In what plants? What parts? Es- 

 sential Oils, their character. Instances. What do they often become on ex- 

 posure to the air? What may such substances be ctmsidered? In what 

 plants do essential oils abound? Id what parts? C.ioutchouc, in what plant;* 

 found ? 



