No. 610] MUTATION THEORY AND SPECIES-CONCEFT 585 



variation, which is perpetuated by heredity and not be- 

 cause the plant has any advantage or disadvantage in life 

 compared with Platy stigma. Only one species of Plat- 

 y stem on (P. calif ornicus Benth.) and two of Platy stigma 

 have been generally recognized, although Greene^ has 

 described some 50 species based on minor differences. 



Another significant difference between Platy stemon 

 and Platystigma is in the variations of the petals. In 

 Platystemon the number varies from 6 to 10 or more, and 

 all the petals of a flower or a plant vary together in color 

 from dark yellow through light vol low to white. In 

 Platystigma, on the other hand, tlie numher of petals ap- 

 pears to be uniiormlv six, and the outer three vary m 

 color independentlv of the (allernato) inner three. Thus 

 jii Platystigma lincarc I'otith. (which Greene calls Hes- 

 p( } 0)>nco}i puhheUnm) tlie oiitei petaK m<n ho daik a el 

 or \\\\\\ a 11101 c oi h c\ton-i\o ^\(m]oo '^liai)ed dark 

 m11()A\ iii.nk ,11 tlu li). the imiei ])etals are light 



vollow or Av]iit(^'^ 



'1 lio iK'ciiliarilv 111 ilic carpels ot Platifstemon acquires 

 addc'l mlcrc>t troiii llio I act that, as Lindley pomted out,** 

 it 1- l'\ no ino.'iii- nil H inc. Imt contraction of the sides of 

 the cMi'itcls. torniiiiii- a toi'iHose structure, has occurred 

 e(iuall\ and miivt hri\e oiminated independenth iii Ifi/pc 

 comn of the Papa\ ei ace.T, in such geneia a- the ladi-hes 

 anions: ('rucifei\T. in Oruithopus among the Lei>-iiiniiios{p, 

 and in other families. AYe may look u])on tins condition 

 as apparently the result of parallel mutation in ditferent 

 families, independent of utility; and countless other cases 

 of a similar kind occur amonir hii>-her plants. 



From the few instances I have cited, which could be 

 added to indefinitelv. an<l 1 rotn tnc nhnndnni cN iiiciir,' (^f 

 marked \aiiation-< ^\lii(h \\( h.i\( lioni .i i it no 



