. Plant anatomy from the standpoint of the development and functions of the tissues, and handbook of micro-technic. Plant anatomy. 42 DIFFERENTIATION OF THE TISSUES from their orginal cellulose composition; but they are some- times decidedly thickened and lignifiied. They are short lived; in woody plants the surrounding bundles crowd in and crush them, and in herbaceous plants they often break down and leave a hollow space; in other cases still they may persist for a long time as dead elements. The pith cells are for some time of use in the storage and slow conduction of water and some- times
. Plant anatomy from the standpoint of the development and functions of the tissues, and handbook of micro-technic. Plant anatomy. 42 DIFFERENTIATION OF THE TISSUES from their orginal cellulose composition; but they are some- times decidedly thickened and lignifiied. They are short lived; in woody plants the surrounding bundles crowd in and crush them, and in herbaceous plants they often break down and leave a hollow space; in other cases still they may persist for a long time as dead elements. The pith cells are for some time of use in the storage and slow conduction of water and some- times they are employed in the storage of food, even after they are several years old, but they are evidently not commonly depended on long for any essential function. The ground meristem lying between the vascular bundles undergoes cell division vertically and transversely and the cells thus formed enlarge and frequently become elongated in the radial direction. In this way the primary medullary rays are formed. The medullary rays have two distinct functions: they carry water and substances in solution radially, inward and outward as needed, and they store water and reserve foods. Since the primary rays extend usually only a few millimeters vertically they are not suited for transporting materials in that direction. A study of cross- sections needs to be supplemented by an ex- amination of vertical tangential sections to make the extent of the medullary rays clear. In these vertical sections it is seen that the primary vascular bundles do not maintain an independent and isolated course through the stem, but anastomose with each other across the upper and lower borders of the rays, as seen in Fig. 20. In the foregoing a type of vascular bundle has been chosen known as the collateral type; where one phloem strand stands radially in front of the xylem strand. While this is the prevailing type, there are others that must not be passed unnoticed here. It sometimes happens that a second p
Size: 978px × 2555px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectplantanatomy, bookyea
