HETEROSTYLY 



47 



Among dimorphous flowers four modes of fertilization are possible, two of them 

 legitimate, and two illegitimate. Darwin has represented the possible legitimate and 

 illegitimate unions by the accompanying diagram (Fig. 5). 



Eighteen modes of fertilization are possible among trimorphous flowers, and of 

 these six are legitimate. If we indicate the longest organs ( 5 and 5 ) by /, the 

 medium ones by m, and the shortest by s, and use a, b, and c to represent the 

 long-styled, medium-styled, and short-styled forms respectively, the six legitimate 

 crossings possible are as follows : 



/ 5 {b) with / 5 . ? $ {a) with rn $ . 



I t, {c) / 5 . m S (c) m $ . 



The twelve illegitimate modes of crossing are : 

 / $ (b) with m 5 . ? J (a) with / 5 . 



/ $ (3) s 2 ''^ ^ (^) " -^ ? 



/ 5 {c) 711 5 . ? S (c-) / 5 . 



/ 5 (<r) J $ . w S (r) J $ . 



The six legitimate modes of crossing have been schematically represented by 

 Darwin in the following manner : 



Fig. 6. Diagram showing the possible legitimate unions in a triniorphic pla^ii {Lythrum 

 Salicaria) (after Darwin). The arrows and dotted lines indicate the anthers from which the pollen 

 must be brought to the stigma of one of the three forms, so as to give a legitimate union with complete 

 fertility (Loew). (i) Long-styled form. (2) Medium-styled form. (3) Short-styled form. 



The results of numerous experiments carried out with the greatest care by 

 Darwin and Hildebrand are as follows (according to Loew, ' Einfiihrung in die 

 Bliitenbiologie,' pp. 218-20): 



