12 Rev. P. Keith on the Structure of Living Fabrics, 



of modern botanists, and the Imperfect plants the Cryptoga- 

 mia of Linnaeus. 



After all this, the reader will perhaps be of opinion that 

 the division of plants into Perfect and Imperfect, is sufficiently 

 well founded to justify our adoption of it, at least in a general 

 and popular survey of the vegetable structure, which it is our 

 object briefly to exhibit, and to which we now proceed, — 

 taking, first, the external structure, and, secondly, the inter- 

 nal structure. 



I. The External Structure. 



If a plant of the perfect class is detached from the soil, 

 and surveyed externally in the season of flowering, it may be 

 perceived, even by the most inattentive observer, to be com- 

 posed of the following distinct parts : the root, the trunk, 

 the branch, the bud, the bulb, the leaf or frond, the flower, 

 the fruit, and perhaps the seed. Of these parts some are 

 temporary, and some permanent ; some conservative, and some 

 reproductive; or, as Mr. Burnett would say, some nutrients, 

 and some generants. 



The Root. — The root, or caudex desce?idens of Linnaeus, is 

 that part of the plant by which it attaches itself to the soil in 

 which it grows, or the substance on which it feeds, and is the 

 principal organ of nutrition. To this definition there are no 

 doubt a good many exceptions. The several species ofLemna 

 or Duck-meat float on the surface of the water, and are not 

 fixed by their roots to any particular spot. Many of the 

 Confervce have no root at all, or, at least, no distinct organ 

 that can be called by that name; while the Truffle (Tuber 

 cibarium) is apparently altogether root. But almost all plants 

 of the higher orders are fixed in the earth by a root, de- 

 scending in species of large growth, and even in many species 

 of small growth, to a considerable depth below the surface, — 

 quae quantum vertice ad auras 



jEthereas, tantum radice in Tartara tendit. — Virg. Georg. ii. 291. 



and spreading by means of lateral divisions to a considerable 

 extent around the centre. The divisions of the root of the 

 Baobab, or African Calabash-tree (Adansonia digitata\ have 

 been known to measure upwards of a hundred feet in length. 



Yet there are many roots which descend into the soil, 

 merely in one single and undivided mass, large at the base, 

 and tapering in a spindle-shaped form to the apex, without 

 either branch or fork, beyond that of a few scattered and 

 thread-like fibres. The Carrot, the Parsnip, and the Radish 

 are well-known examples. Roots of this species are some- 

 times found to terminate abruptly, as if cut or bitten off* at 



