Book I. 



INTERNAL STRUCTURE OF PLANTS. 



213 



esteemed for the rich and delicate flavor which it imparts to soups and sauces ; and the 

 mushroom {^Jig. 222.) and morel [jig. 223. ) for their esculent property, and utility in the 

 preparation of ketchup. ^ 223 



Sect. IIL Of the Inteinal Structure of Plants. 



1311. The organs of plants discoverable by external exami7iation, are themselves reducible 

 in component organs, which are again resolvable into constituent and primary organs. 

 These are called the decomposite, the composite, and the elementaiy. 



SuBSECT. 1. Decomposite Organs. 



1312. The decomposite organs constitute the vegetable individual, and are distinguishable 

 on external examination ; to the dissection of which we will now proceed, in the order of 

 the seed, pericarp, flower, leaf, gem, and caudex, or branch, stem, and root, with their de- 

 composite appendages. 



1313. The seed. The mass of the seed consists of two principal parts, distinguishable without much dif- 

 ficulty ; namely, the integuments and nucleus, or embryo and its envelopes. 



1314. The integuments proper to the seed are two in number, an exterior integument and an interior in- 

 tegument. 



1315. The exterior integument, or testa, is the original cuticle of the nucleus, not detachable in the early 

 stages of its growth, but detachable at the period of the maturity of the fruit, when it is generally of a 

 membranaceous or leathery texture ; though sometimes soft and fleshy, and sometimes crustaceous and 

 bony. It may be very easily distinguished in the transverse or longitudinal section of the garden-bean or 

 any other large seed. 



1316. The interior integument,'or sub-testa, lines the exterior integument, or testa, and immediately en- 

 velopes the nucleus. Like the testa, to which indeed it adheres, it may be easily distinguished in the 

 garden-bean {Jig. 224.), or in a ripe walnut ; in which last it is a fine transparent and net-like membrane. 



1317. The nucleus is that part of the seed which is 

 contained within the proper integuments, consisting 

 of the albumen with the vitellus, when present, and 

 embryo. 



1318. The albumen is an 'organ resembling in its 

 consistence the white of an egg, and forming, in most 

 cases, the exterior portion of the nucleus, but always 

 separable from the interior or remaining portion. 



1319. The vitellus is an organ of a fleshy but firm 

 contexture, situated, when present, between the al- 

 bumen and embryo; to the former of which it is 

 attached only by adhesion, but to the latter by incor- 

 l)oration of substance, so as to be inseparable from it, 

 except by force. 



1320. The embryo {a), which is the last and most 

 essential part of the seed and final object of the 

 fructification, as being the germ of the future i)lant, is a small and often very minute organ, enclosed 

 within the albumen and occupying the centre of tlie seed. 



1321. The cotyledon or seed-lobe (6), is that portion of the embryo that encloses and protects the plant- 

 let, and springs up during the process of germination into what is usually denominated the seminal leaf, 

 if the lobe is solitary ; or seminal leaves, if there are more lobes than one. In the former case the seed 

 is said to be monocotyledonous ; in the latter case, it is said to be dicotyledonous. Dicotyledonous seeds, 

 which constitute by far the majority of seeds, are well exemplified in the gardon-bean. As there are 

 some seeds whose cotyledon consists of one lobe only, falling snort of the general number, so there are 

 also a few whose cotyledon is divisible into several lobes, exceeding the general number. They have been 

 denominated polycotyledonous seeds, and are exemplified in the case of lepidium sativum or common 

 garden-cress, in which the lobes are six in immber ; as in that also of the different species of the genus 

 pinus, in which they vary from three to twelve. 



1322. The plantlef, or future plant in miniature, is tlie interior and essential portion of the embryo, and 

 seat of vegetable life. In some seeds it is so minute as to be scarcely perceptible ; while in others it is so 

 large as to be divisible into distinct parts, as in the garden-bean. 



1323. The pericarp,.vi\nch in different species of fruit assumes so many varieties of contexture, acquires 

 its several aspects, not so much from a diversity of substance as of modification. 



1324. The valves of the capsule, but particularly tiie partitions by which it is divided into cells, are com- 

 posed of a thin and skinny membrane, or of an epidermis covering a pulp more or less indurated, and in- 



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