1909] LEAVITT—HOMOEOSIS IN PLANTS 



53 



tion is not retrograde in any except an imaginary sense; since the 



normal 



conservative, as compared with the tentaculiferous leaf; and the ovule 

 as vastly more ancient than the tentacle into which it suffers change. 

 In peloria the morphogenetic relations are not so instantly obvious. 

 However, the phenomenon is usually, if not always, better viewed as 

 a homoeotic, than as an atavistic, occurrence. In notices of peloric 

 monstrosities one often meets with the statement that these forma- 

 tions have a historical value. Thus, with respect to a peloric 

 Laelio-Cattleya, Masters^ suggests that here is a reversion to the 

 earlier and simpler conformation from which the peculiar orchid 

 structure, as we know it, has evolved. While this is true abstractly, 

 in a merely descriptive sense— since actinomorphy doubtless preceded 

 zygomorphy in the monocotyledonous phylum— yet it is probably 

 untrue if we are to take it in any real phylogenetic sense, with the 

 understanding that actinomorphy has remained latent as a heredi- 

 tary character through the enormously long period of the evolution 

 of this family from an actinomorphic condition. Regular peloria is 

 Jo be considered in conjunction with the opposite change, which 

 frequently occurs in orchids. The antithesis of the two pelorias 



a-es it evident that we have here something besides atavism; since 

 1 either form is atavistic the other cannot be. This outcome, 

 coupled with the fact that we have a less objectionable construction, 



"credits the entire idea of reversion in peloric orchids. The argu- 

 ment extends to other families. 



of t ^ lth ° Ut further ex Patiation, it will be evident— if the standpoint 

 abu^H^ 56111 PapCr iS correct ~ that the word reversion is a much- 

 call ' t ^ rm " Tme reversions > except those which occur periodi- 

 to be m 0nto S enesis > are, I suspect, rather rare. Atavism is never 

 onlv 6 a ! SUmed off " hand in teratological cases, but it is to be admitted 

 borne r 6Stablished h y aid of independent proof. It should be 

 often 1 1 \ mmd that antecedents °f monstrous forms are much more 

 ditim, 6 S ° Ught m contemporary normal parts titan in ancestral con- 



di 



ions. 



botanical 



naxp values 



37 g! ?L m botanical th eory in at least three different relations 



