37. Stem of Monocotyledon, section of. 38. Seed of Shepherd’s Purse, transverse section. 39. Stamen of Chickweed. 40. Stigma of Chickweed. 41. Ovary of Chickweed. 42. Leaf of Chickweed. 43. Seed of Wallflower, section of. 44. Seed of Wallflower, radicle and cotyledons. 45. Embryo-sac of Chickweed. 46. Embryo-sac of Chickweed. 47. Embryo-sac of Chickweed. 48. Wheat, cotyledon and leaves of, section. 49. Mustard-seed, cotyledons and radicle. 50. Mustard-seed, transverse section. 51. Chickweed, seed of. 52. Seed of _Eccremocarpus scaber_. 53. Grain of Wheat: _a_, cotyledon; _b_, embryo; _c_, radicle; _d_, albumen. 54. Ovule of Wallflower. 55. Cotyledons of Chickweed. 56. Plum-stone, section of. A TEXT-BOOK OF THE MICROSCOPE. CHAPTER I. THE MICROSCOPE. The microscope (from μικρὁς, little, and σκοπέω, to see), so called because it enables us to see objects which are too small to be seen with the naked eye, consists of several parts, each of which has its special use. As the proper management of these is of great importance in the successful application of the instrument to minute investigations, we shall commence with the consideration of their names and uses, including those of the more important pieces of accessory apparatus. _Microscope._--The foot of the microscope is that part which supports the instrument upon the table; it is connected above with the stand, of which it is often considered a part. The stand sometimes consists of a single rod or pillar; but in the best microscopes it is composed of two upright plates, between which, at the upper part, the rest of the microscope swings stiffly upon an axle. Arising from this axle, indirectly through the medium of parts which require no special mention, is an arm, to which the body is fixed. The body is moveable up and down by one or two large milled heads, connected with a grooved rod or pinion, which works in the teeth of a rack fixed to the back of the body, or of the arm which supports the body. The large milled heads form the “coarse movement,” as it is called. On the top of the arm, or on the front and lower part of the body of the microscope, is placed the “fine movement,” consisting of a small milled head, with a fine screw, for moving the body through very small distances. Next is the “stage,” or flat plate, upon which the objects to be viewed are placed. This is often so arranged that, by turning two milled heads, the object can be moved backwards and forwards, or from side to side; it is then a “moveable stage.” The eye-piece slides into the upper end of the body; and the object-glass screws into its lower end. Beneath the stage is the mirror, which reflects the light through the object, the object-glass, and eye-piece to the eye.