MUTILATION AND REGENERATION 417 



are rare, but in the triton a new lens is easily regenerated 

 and in some of the lower batrachia young individuals 

 may regenerate a whole eye. Still lower animals are 

 capable of regenerating the head, including the brain 

 and eyes, but the organs in such cases are simple and do 

 not form counterparts of the complex brains and eyes 

 of the vertebrates. When the heart is a simple con- 

 tractile tube slowly propelling the blood through vessels 

 not terminating in capillaries, the viscus may be dis- 

 pensed with for some time, during which a new one may 

 be provided, but when, as in the vertebrates, it is an 

 elaborately specialized pump with complexly arranged 

 chambers and valves and when the somatic life is main- 

 tained solely through the circulating blood, the heart 

 cannot be dispensed with at all. 



REGENERATION IN PLANTS. 



This subject is best considered under two separate 

 headings: 1. The repair of damage; 2. The restoration 

 of lost parts. 



1. The repair of damage done to plants is effected 

 through changes in the cells injured but not destroyed. 

 The destroyed cells die, become brown and dry, and 

 drop off. The walls of the underlying cells then become 

 lignified or wooden and the more delicate cells below 

 thus protected. Such changes at the cut edge of a leaf 

 protect the remainder, which lives on in its deformed 

 state for a long time. In the case of tubers, as, for ex- 

 ample, potatoes, similar changes take place in the cut 

 surfaces and thus prevent destruction of the buds 

 which remain alive, so that cut fragments of seed potatoes 

 may be kept for several, days before planting, the buds 

 remaining vital and beginning to grow when favorable 

 opportunities are afforded. 



The wooden stems of higher plants when super- 

 ficially injured are repaired by an active growth of the 

 living cells round about the seat of injury, forming a 

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