. Nature and development of plants . n. of a root of corn i 17 in. in diameter, and230 on a square mm. of a pea rt surfa 24. The Structure of the Root.—You have noticed that onlytlu- apical portion of the root elongates and it may be well to first examine the structure of this region in order to see how growth is brought about and what changes are effected by it. The tipof the root is composed of very delicate cells. Certain of thesecells are rapidly dividing by forming new walls through the middle of the cells, thus dividing each cell into two new cells. The division of a cell is effected in
. Nature and development of plants . n. of a root of corn i 17 in. in diameter, and230 on a square mm. of a pea rt surfa 24. The Structure of the Root.—You have noticed that onlytlu- apical portion of the root elongates and it may be well to first examine the structure of this region in order to see how growth is brought about and what changes are effected by it. The tipof the root is composed of very delicate cells. Certain of thesecells are rapidly dividing by forming new walls through the middle of the cells, thus dividing each cell into two new cells. The division of a cell is effected in a very elaborate manner. Thefirst indication of this growth appears in the nucleus. This organof the cell enlarges ( Fig. 31, A) and we now see that it has a very ch. Fig. 31. Cell division in root of corn: ./, cell with nucleus enlipreliminary to division—/, linin; ch, chromatin. The central . later stage, the chromatin has increased and appearsribbon-like k- in. C, formation of the chromosomes, cr. D, formation ofthe spindle and the arrangement of the chromosomes in the center of thes|)in. < Cardiff. complex structure, consisting of a protoplasmic mass surroundedby a delicate membrane and traversed b\ a network of delicatethreads (linin) and containing one or more large granules (nu-cleoli). The most importanl portions of the nucleus arc theminute particles (chromatin) which are associated with the lininthreads. It has been supposed that this substance controls the NATURE OF PLANTS 49 activity of the cell and determines the kind of cell that shall beformed and the work that it shall perform. As the nucleusenlarges the chromatin increases in amount and often forms aribbon-like structure (Fig
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