A practical course in botany : with especial reference to its bearings on agriculture, economics, and sanitation . e cambium, C. In this positionthe growing cambium adds new cells to the inner side of thephloem, and to the outer side of the xylem, so that the formergrows on its inner face and the latter on its outer. In peren-nial plants, as new rings are added to the xylem from seasonto season, the older anes die and are changed into heartwood,which thus gradually increases in thickness till in some of thegiant redwoods and eucalypti, it may attain a diameter ofthirty-five or forty feet. In t
A practical course in botany : with especial reference to its bearings on agriculture, economics, and sanitation . e cambium, C. In this positionthe growing cambium adds new cells to the inner side of thephloem, and to the outer side of the xylem, so that the formergrows on its inner face and the latter on its outer. In peren-nial plants, as new rings are added to the xylem from seasonto season, the older anes die and are changed into heartwood,which thus gradually increases in thickness till in some of thegiant redwoods and eucalypti, it may attain a diameter ofthirty-five or forty feet. In the phloem, on the other hand,as new cells are added from within, the older ones aregradually changed into hard bast, h, then into bark, andare finally sloughed off and fall to the ground. It is thisfree line of communication with the active cambium thatenables dicotyl stems to grow on indefinitely, the sheath, e,being formed on the exterior face of the bundles only, leav-ing the other free, whence they are said to be drawings of cross and vertical sections of a dicotyl 106 PRACTICAL COURSE IN BOTANY. Fig. 122. — Internal structure of a pine stem, showing longitudinal section of afibrovascular bundle through a medullary ray, sm, sm : s, tracheids; t, borderedpits, surface view; c, cambium; v, sieve tubes; vt, sieve pits, analogous to thesieve plates in dicotyl stems. stem as it appears under the microscope, labeling correctlyall the parts observed. Show the shape and relative size of the different cells. Com-pare your drawings withthose made in your studyof monocotyl stems, andwrite in your notebook theessential points of differencebetween the two. 117. The stems of coni-fers, the group of Gymno-sperms to which the pinebelongs, do not differ greatlyfrom those of dicotyls, thechief difference being thatthe vascular bundles containtracheids only, correspond-ing to the smaller vessels of
Size: 1897px × 1317px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpublisher, booksubjectplants
