Page:Encyclopædia Britannica, first edition - Volume I, A-B.pdf/66

 44 A G R I C I Plate V, Fig. 2. H, The third year’s growth. I I I, The true wood. K K, The great air-veffels,. L L, The leffer ones. M M M, The parenchymatous infertions of the bark reprefented by the white rays. N, O, The pith, with its bladders or cells. Sect. IV. Of the Leaves. The leaves of plants confift of the fame fubftance with that of the trunk. They are full of nerves, or woody po/tions, running in all directions, and branching «ut into innumerable fmall threads, interwoven with the Parenchyma like fine lace or gauze. The (kin of the leaf, like that of an animal, is full of pores, which both ferve for perfpiration, and for the abforption of dews, air, fcc. Thefe pores, or orifices, differ both in (hape and magnitude in different plants, which is the caufe of that variety of texture or grain peculiar to every plant. The pulpy or parenchymatous part, corififts of very minute fibres, wound up into fmall cells' or bladders. Thefe cells are of various fizes in the fame leaf. All leaves, of whatever figure, have a marginal fibre, by which all the reft are bounded. The particular (hape of this fibre determines the figure of the leaf. The veffels of leaves have the appearance of inofcula,ting; but, when examined by the microfcppe, they are found only to be interwoven, or laid along each other. What is called air-veffels, or thofe which carry no fap, are vifible even to the naked eye in fome leaves. When a leaf is (lowly broke, they appear like fmall woolly fibres, connected to both ends of the broken piece. Plate VI. Fig. 1. The appearance of the air-veffels to the eye, in a vine leaf drawn gently afunder. Fig 2. A fmall piece cut off that leaf. Fig. 3. The fame piece magnified, in which the veffels have the appearance of a fcrew. Fig. 4. The appearance of thefe veffels as they exift in the leaf before they are ftretched out. Sect. V. Of the Flower. It is needlefs here to mention any thing of the texture, or of the veffels, ire. of flowers, as they are pretty fimilar to thofe of the leaf. It would alfo be foreign to our prefent purpofe, to take any notice of the characters and diftindtions of flowers. Thefe belong to .the fcience of Botany, to which the reader is referred. There is one curious fad, however, which muft not be omitted, viz. That every flower is perfe&ly formed in all its parts many months before it appears outwardly ; that is, the flowers which appear this year, are not, pro-

L T U R E. perly fpeaking, the flotvers of this year, but of the laft. For example, mezereon generally flowers in January; but thefe flowers were completely formed in the month of Auguft preceeding. Of this faft any one may fatisfy himfelf by feparating the coats of a tulip root about the beginning of September; and he will find that the two innermoft form a kind of cell, in the centre of which (lands the young flower, which is not to make its appearance till the following April or May. Plate VI. Fig.;. Exhibits a view of the tulip-root when diffeCled in September, with the young flower toward* the bottom. S E c T. VI. Of the Fruit. In deferibing the ftrudure of fruits, a few examples (hall be taken from fuch as are mod generally known. 1. A Pear, befides the (kin, which is a production of the (kin of the bark, confifts of a double parenchyma or pulp, fap, and air-veffels, calculary, and acetary. The outer parenchyma is the fame fubftance continued from the bark, only its bladders are larger and more fucculent. It is every where interfperfed with fmall globules or grains, and the bladders refpeCl thefe grains as a kind of centres, every grain being the centre of a number of bladders. The fap and air-veffels in this pulp are extremely fmall. Next the core is the inner pulp or parenchyma, which confifts of bladders of the fame kind with the outer, only larger and more oblong, cprrefponding to thofe of the pulp, from which it feems to be ^derived. This inner pulp is much fourer than the other, and has none of the fmall grains interfperfed through it; and hence.it has got the name of acetary. Between the acetary a^nd outer pulp, the globules or grains begin to grow larger, and gradually unite into a hard ftony body, efpecially towards the corculum, or (tool of the fruit; and from this circumftance it has been called the calculary. Thefe grains are not derived from any of the organical parts of the tree, but feem rather to be a kind of concretions precipitated from the fap, fimilar to the precipitations from wine, urine, and othei liquors. The core is a roundiflt cavity in the centre of the pear, lined with a hard woody membrane, in which the feed is inclofed. At the bottom of the core there is a fmall duCt or canal, which runs -up to the top of the pear; this canal allows the air *0 get into the core, for the purpofe of drying and ripening the feeds. Plate VII. Fig. I. A tranfverfe fe&ion of a pear, as it appears to the naked eye. A, The (kin, and a ring of fapveffels B, The outer parenchyma, or pulp.