CHAP. VI. ON HETEROSTYLED PLANTS. 253 



of the two forms should differ in size relatively tq the 

 length of the pistil which the tubes have to penetrate, 

 but that in the latter case it would not be necessary 

 that the grains should thus differ. Whether this expla- 

 nation can be considered satisfactory must remain at 

 present doubtful. 



There is another remarkable difference between 

 the forms of several heterostyled species, namely in the 

 anthers of the short-styled flowers, which contain the 

 larger pollen-grains, being longer than those of the 

 long-styled flowers. This is the case with Hottonia 

 palustris in the ratio of 100 to 83. With Lvmnan- 

 themum Indicum the ratio is as 100 to 70. With the 

 allied Menyanthes the anthers of the short-styled form 

 are a little and with Villarsia conspicuously larger 

 than those of the long-styled. With Pulmonaria an- 

 gustifolia they vary much in size, but from an aver- 

 age of seven measurements of each kind the ratio 

 is as 100 to 91. In six genera of the Eubiaceae there 

 is a similar difference, either slightly or well marked. 

 Lastly, in the trimorphic Pontederia the ratio is 100 

 to 88; the anthers from the longest stamens in the 

 short-styled form being compared with those from the 

 shortest stamens in the long-styled form. On the other 

 hand, there is a similar and well-marked difference 

 in the length of the stamens in the two forms of 

 Forsythia suspensa and of Unum flavum; but in these 

 two cases the anthers of the short-styled flowers are 

 shorter than those of the long-styled. The relative 

 size of the anthers was not particularly attended to in 

 the two forms of the other heterostyled plants, but 

 I believe that they are generally equal, as is certainly 

 the case with those of the common primrose and 

 cowslip. 



The pistil differs in length in the two forms of every 



