268 



ELEMENTARY BIOLOGY 



321. Regeneration. A small piece of a begonia leaf, placed 

 in close contact with moist soil, puts forth tiny roots that 

 grow into the soil ; and a tiny bud is formed, which starts 



to grow into a shoot. In other words, 

 it is possible to get a whole plant 

 from a part of a plant. A part of 

 the leaf takes on a new mode of 

 growth, producing root cells and stem 

 cells where under ordinary conditions 

 there would have been reproduced 

 only more leaf cells (see Fig. 13), 



If the fore part of an earthworm 

 is cut off, a new fore part is 

 formed ; or if the hind end is re- 

 moved, a new "tail" may be grown 

 (Fig. 106). This process of regrow- 

 ing a lost part is called regeneration, 

 and is in some ways similar to the 

 healing of a wound, only it goes 

 much farther. 



Regeneration takes place to a larger 

 or smaller extent in all kinds of ani- 

 mals under normal conditions of life 

 that lead to mutilations of various 

 kinds. A single ray of a starfish will 

 be regenerated, or even two or three 

 rays (see Fig. 107). 



Salamanders have regenerated tails 

 lines show where the cut was and Icgs, and the tritou, ouc of the 

 made. The shaded portions rep- jj^ards, Can regenerate the eye. In 



resent the new growths. (After ^ ■' 



Morgan) general, however, the higher or more 



specialized organs are not readily 



regenerated, and the highest animals do not regenerate as 



readily as do lower animals. A finger cut from your hand will 



not be regenerated, although the stump may heal up. And 



a b 



Fig. 106. Regeneration in 

 earthworms 



«■, worm from which the anterior 

 end had been cut off ; b, worm 

 from which the posterior end 

 had been cut off. The dotted 



