220 REPRODUCTION IN PLANTS AND ANIMALS 



Pleurococcus. Cell 

 division by simple 

 fission. 



plant. Examined under the microscope, specimens may be 

 found showing two, three, four, or more cells. In our study of 

 the amoeba we found that a single cell forms 

 two by division. In this process the nucleus 

 divides first, then the cell body begins to split, 

 and eventually two cells are formed, each half 

 the bulk of the original cell. 



Cell Division results in Growth in Size. — 

 Animals and plants grow larger by a multipli- 

 cation of the cells, which are cemented together 

 to form tissues. The saying " great oaks from 

 little acorns grow " illustrates this fact. The 

 growth of roots, buds, leaves, and seeds, the 

 development of a kitten, and the shooting up of a boy or a girl at 

 adolescence are examples of rapid cell division. 



New Plants may be formed by Cell Division. — It is a matter 

 of common knowledge that when a chestnut or a poplar tree is 

 cut down, young shoots come up from around the cut stem. 

 New geranium plants may be grown from " slips " or cuttings 

 from the old plant. Sugar cane and the banana plant are propa- 

 gated entirely in this way, not from seeds. Grape vines, straw- 

 berry plants, and many others take root where the stem comes 

 in contact with the soil. Many grasses, like the couch or quick 

 grass, become pests because they spread with such rapidity from 

 their underground stems. Ferns and other plants have under- 

 ground rootstocks which form new shoots 

 that become new plants. Tubers, as the 

 potato, and bulbs, as the onion or hly, are 

 other examples of vegetative growth known 

 as vegetative propagation. 



Regeneration. — In certain animals, lost 

 parts grow again by cell division. A flat- 

 worm may be cut into as many as twenty 

 pieces, each one of which will grow into or 

 regenerate sl new worm. Earthworms re- 

 generate lost segments and starfish lost rays. 



Crustacea regenerate lost antennae or other appendages ; it is com- 

 mon for the fiddler crab, when caught, to drop a claw in order to 



Regeneration. A star- 

 fish that has lost one of its 

 rays will grow a new one. 



