34 



A DISCOURSE 



BOOK I. both the growth and substance of what the earth produces, sensibly 

 altering- their qualities, if some friendly and genial heat be wanting to 

 exert the prolific virtue. Thus we find, that the hot and warmer regions 



clearly understood, it will be necessary to observe, that the lobes of most farinaceous 

 grains are fixed in the earth : They are therefore improperly termed seminal leaves, being 

 rather the placenta, or cotyledons of the plant. On the contrary, vegetables that have an 

 oily seed, as rape, hemp, line, and turnip, carry their lobes upwards, and spread them upon 

 the surface, in the form of broad leaves. These, though they perform the office of a placenta, 

 are properly seminal leaves; and to this distinction I shall adhere. Fig. 1. represents 

 the body, or placenta, of a bean, with its germ, radicle, umbilical chord, and ramifications. 

 a. The germ. b. The body, or placenta, with the umbilical chord and ramifications, 

 c. The radicle. Fig. 3. represents the placenta, or sepd-leaves, of a turnip, with its 

 radicle and germ. a. The germ. b. The placenta, or seed-leaves. c. The radicle. 

 Fig, 2. represents the germ of a grain of wheat, with its root and capsule, containing the 

 milky juice for the nourishment of the tender plant, a. The origin of the crown from 

 whence the second roots spring, b. The pipe of communication between the first roots and 

 the crown, which in this early stage of the plant is covered with a membranous sheath. 

 c. The grain with its first toots. As soon as the coronal, or spring root, puts out, the pipe 

 of communication throws off its covering, and appears naked, as in Fig. 4. b. — Regarding 

 these two kinds of roots, the economy of Nature is wonderful. , The seminal root, lying 

 deep, nourishes the tender plant during the severity of winter ; but when the spring comes 

 on, and it is necessary that the plant should advance in size, the coronal root then shoots 

 forth and spreads its fibres just within the surface, where the land is always the richest. 

 When the seed happens to be buried very deep. Nature lengthens the pipe of com- 

 munication, and on no account will form the crown, from whence the spring roots are 



sent forth, till the surface is obtained : Fig. 4. 1 believe I do not err when I call this 



vegetable instinct. To illustrate the subject of vegetation, let us take a view of what 

 happens to a bean after it has been committed to the earth. In a few days, sooner or 

 later, according to the temperature of the weather and disposition of the soil, the external 

 coverings open at one end, and disclose to the naked eye part of the placenta, or body 

 of the grain. This substance consists of two lobes, between which the seminal plant is 

 securely lodged. Soon after the opening of the membranes, a sharp-pointed body appears; 

 This is the root. By a kind of principle, which seems to carry with it some appearance of 

 instinct, it seeks a passage downwards, and fixes itself into the soil. At this period the 

 root is a smooth and polished body, and perhaps has but little power to absorb any thing 

 from the earth, for the nutriment of the germ. The two lobes now begin to separate, 

 and the germ, with its leaves, may plainly be discovered. As the germ increases m size, 

 the lobes are further separated, and the tender leaves being closely joined, push themselves 

 forward in the form of a wedge. These leaves take a contrary direction "'to the root. 

 Influenced by the same miraculous instinct, if I may be allowed the expression, they seek 

 a passage upward, which having obtained, they lay aside their wedge-like form, and 



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