68 HEREDITARY CHARACTERS 



only in a graft or cutting, but even in a part of the same 

 plant. A very good example of this is the nectarine, which 

 is a variation appearing on a peach-tree. The variation 

 occurs somewhat as follows: On a peach-tree which has 

 hitherto always produced rough-skinned fruit, a branch 

 appears which bears the smooth-skinned fruit that has 

 been called the nectarine. This branch will go on bearing 

 nectarines and not peaches, and trees produced from cuttings 

 from it will also produce nectarines, although of course a 

 further variation may take place back to the original rough- 

 skinned fruit. It is thus evident that inborn variations may 

 occur in a part of a plant in a manner that is inconceivable 

 in the case of the higher animals. 



This property exhibited by plants, of reproducing all the 

 tissues and organs necessary to form a new individual from 

 a small portion cut off from an existing individual, is 

 exhibited among some of the lower animals. Among uni- 

 cellular forms it is usual, if the animal be cut into several 

 pieces, for all those which contain a portion of the nucleus 

 to form a new animal complete in all its parts. Among the 

 lower multicellular forms, such as Hydra, this also happens, 

 but the complete phenomenon is not present in the higher 

 animals. Thus in many plants, and among some of the lowest 

 multicellular animals, we find that all the cells of the body, 

 even those which are most differentiated, retain the potenti- 

 ality of producing all the other cells forming the various tissues 

 of the body, including the reproductive cells. As we go higher 

 up the animal scale, however, we find this potentiality is 

 more and more limited. It still exists to a certain extent 

 even among vertebrates, some of which will grow new limbs 

 or organs containing all the various tissues involved, upon 

 the destruction by accident of the original limb. One of the 

 most remarkable instances of this kind is the way in which the 

 lens in the eye of the salamander is reproduced after removal. 1 



1 Wolff, Gustav, " Die Regeneration de Urodelenlinse," Archiv fur Entwick- 

 lungsmcchanik, i. 3, 1895 ; Muller, E., " Uber die Regeneration der Augenlinse 

 nach Exstirpation derselben bei Triton," Archiv fur mikroscopischc Anatomie, 

 xlvii. 1, 1896. 



