'909] LEAVITT—HOMOEOSIS IN PLANTS 6 7 



nary conditions only the differential determinants are free to influence 

 the development of the cell and its activities, the regenerative or 

 reserve determinants being held strictly under restraint until they are 

 called for, to reconstruct lost members. 



Homoeosis has a similar influence with regeneration upon the 

 Roux-Weismann idea; and perhaps a 



more 



very 



varied and abundant. And if the vast array of data, the existence of 

 which has been suggested in the present article, is added to the evidence 

 from regeneration, the necessity for providing full reserve-funds of 

 determinants in differentiated parts is much increased. Many parts 

 of the body— this statement is made especially with reference to 

 plants-are able to produce almost any other part. We are prob- 

 ably warranted in postulating a pangenerative capacity for every 

 vital member. We know that a single epidermal cell of the leaf in 

 Begonia may originate a complete plant. Indications are not wanting 

 that single living plant cells in general intrinsically possess the same 

 Power ordinarily latent, its exercise inhibited by circumstances. 

 ^ each cell possesses a complete character-fund, the characters 



th l °i bemg S6Verally activated upon motion of factors external to 

 e cell, does not the necessity for imaging special individualized 



celkH r 3 dlSappear ? Can we not as wel1 think tha t differences in 

 s and forms of organs spring from the nature of the molecule of the 



seat f m§ Substance (P r °bably chromatin) , this substance being the 

 „._•_ ° , mor Phogenetic powers ready to be evoked and responding 



nditions in which, in the course of develop- 

 itself placed ? Obviously, in proportion as 



form-giv 



vanou 



—j ~ mc ui verse C( 



"jent, the substance finds 



allrplkrrf 



kind, nf * need of assum ing the existence of different 



Whatev g ™ g SUbstance dimini sh. 

 evolutionwh' ^ ^ ^^ assumed for a n explanation of the micro- 

 form-controllia ** ^ onto S enesi s— whether the existence of special 

 Molecules 10 bodles > or the general properties of the organic 



°ther basisZh° rgan " f0rming StUffS ° apable of diffusion > or some 

 formation of ^^ diversion of formative currents and trans- 

 fre quent an m6mberS into otners of usually dissimilar origin, the 



PPearance of forms in locations not expected in the ordi- 



