. Essentials of biology presented in problems. Biology. 148 THE VARIOUS FORMS OF PLANTS Careful study shows the presence of strands held in the body of the cell by strands of protoplasm, the remainder of the space within the cell being occupied by the cell sap. Pond scum may grow by a simple division of the cells in a fila- ment. This method of asexual reproduction is the way growth takes place in the cells of the root, stem, or leaf of a flowering plant, but another method of reproduction is also seen in pond scum. The cells of two adjoining filaments may push out tubes which meet, thus conne
. Essentials of biology presented in problems. Biology. 148 THE VARIOUS FORMS OF PLANTS Careful study shows the presence of strands held in the body of the cell by strands of protoplasm, the remainder of the space within the cell being occupied by the cell sap. Pond scum may grow by a simple division of the cells in a fila- ment. This method of asexual reproduction is the way growth takes place in the cells of the root, stem, or leaf of a flowering plant, but another method of reproduction is also seen in pond scum. The cells of two adjoining filaments may push out tubes which meet, thus connecting the cells with each other. Meantime the protoplasm of the cells thus joined condenses into two tiny spheres; the bands of chlorophyll are broken down, and ulti- mately the contents of one of the cells passes over the tube and mingles with the cell of the neigh- boring filament, with which it was previously con- nected by the tube formed from the cell walls. The result of this process of fusion is a thick- walled resting cell which we call a zygospore. Conjugation. — The process in which two cells of equal size unite to form a single cell is called conjugation. It is believed to be a sexual process which corresponds in a way to the fertilization in the higher plants.^ This cell thus formed can ^^dthstand considerable extremes of heat and cold, and may be dried to such an extent that it is found in dust or in the air. Under favorable conditions, this spore will germinate and produce a filament. Pleurococcus. — Many other forms of algsB are well known to us. One of the simplest is -^s^is' r> pleurococcus. This little plant consists of a -di ^ . i h • , ^- ,, , . , , ,. . FleuTococcus. A, single cell; single tiny cell, which by division may give ^ .^lony of four cells rise to two, three, four, or even more cells formed from the original which cling together in a mass. The green cell Conjugation of Spirogyra; zs, zygospore; /, fusion in progress. ' Material which
Size: 1000px × 2500px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectbiology, bookyear1911
