. La classificazione delle piante da fiore. Ion era parallela e, tranne che nelle specie a foglie strette, le vene sono state ripetute. Il tipo generale di struttura dello stelo era quello di aConifer ma richiamando i cicadi nel grande pith. Il legno ha solo sviluppo centrifugo, il protoxylem giacente sul lato accanto al pith. Gli elementi di legno erano radiallyarrangiati; lo xilema secondario somigliava strettamente a quello di Araucaria, da dove i gambi fossili erano precedentemente detti Araucarioxylon. Le fosse delimitate, che si verificano solo su pareti teradiali, erano denselv affollate in file alternate, theBorders h.

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. The classification of flowering plants. ion was parallel and, except in the narrow-leaved species, the veins were repeatedlyforked. The general type of structure of the stem was that of aConifer but recalling the Cycads in the large pith. The woodshewed only centrifugal development, the protoxylem lying onthe side next the pith. The wood-elements were radiallyarranged; the secondary xylem closely resembled that ofAraucaria, whence the fossil stems were previously namedAraucarioxylon. The bordered pits, which occur only on theradial walls, were denselv crowded in alternating rows, theborders having an hexagonal outline. Annual rings cannot bedistinguished. The medullary rays were narrow. The phloemhad a similar radial arrangement, and contained sieve-tubes, parenchyma, and sometimes also bast-fibres. The cortical 44 FLOWERING PLANTS [CH parenchyma was traversed by secretory sacs, and strengthenedby hypodermal, radial bands of fibres; the leaf-trace was oftena double bundle. A thick and complicated bark covered thelarger stems.. Fig. 1. Cordaites. A. Longitudinal section of a male cone shewing bracts and stamens (as at /), the latter bearing pollen-sacs (as at e) x 3. B. A stamen more highly magnified bearing four pollen-sacs, that on the righthas dehisced. A vascular bundle runs up the filament and branches belowthe pollen-sacs. C. Longitudinal somewhat tangential section of a female cone shewing thebracts, in the axil of two of which are ovuliferous shoots; a, axis ofovuliferous shoot bearing a lateral bracteole (b) and a terminal ovule;i, outer integument; n, nucellus. D. Apex of ovule more highly magnified shewing canal leading to pollen-chamber; i, dilated cells of integument; jj, pollen-grain. E. Transverse section of leaf, e, epidermis below which are supporting layersof sclerenchyma, s, more strongly developed opposite the two mesarchvascular bundles. The bundles are surrounded by a sheath, sh; in theleft-hand bundle are indicated the centripetal xylem a, the p

Parole chiave associate all'immagine

• bookcentury1900
• bookdecade1900
• booksubjectbotany
• bookyear1904