CiiAP. VI, ON HETEROSTYLED PLANTS. 253 



iieterostyled plant, and although a similar difference 

 is very general with the stamens, yet in the two 

 forms of Linum grandiflorum and of Cordia they are 

 equal. There can hardly be a doubt that the rela- 

 tive length of these organs is an adaptation for the 

 safe transportal by insects of the pollen from the one 

 form to the other. The exceptional cases in which 

 these organs do not stand exactly on a level in the two 

 forms may probably be explained by the manner in 

 which the flowers are visited. With most of the 

 species, if there is any difference in the size of the 

 stigma in the two forms, that of the long-styled, what- 

 ever its shape may be, is larger than that of the short- 

 styled. But here again there are some exceptions to 

 the rule, for in the short-styled form of Leucosmia 

 Burnettiana the stigmas are longer and much narrower 

 than those of the long-styled ; the ratio between the 

 lengths of the stigmas in the two forms being 100 to 60. 

 In the three Rubiaceous genera, Faramea, Houstonia 

 and Oldenlandia, the stigmas of the short-styled form 

 are likewise somewhat longer and narrower ; and in 

 the three forms of Oxalis sensiiiva the difference is 

 strongly marked, for if the length of the two stigmas 

 of the long-styled pistil be taken as 100, it will be 

 represented in the mid- and short-styled forms by 

 the numbers 141 and 164. As in all these cases the 

 stigmas of the short-styled pistil are seated low down 

 within a more or less tubular corolla, it is probable 

 that they are better fitted by being long and narrow 

 for brushing the pollen off the inserted proboscis of 

 an insect. 



With many heterostyled plants the stigma differs 

 in roughness in the two forms, and when this is the 

 case there is no known exception to the rule that the 

 papillae on the stigma of the long-styled form are longer 



