122 HETEROSTYLED DIMORPHIC PLANTS. CHAP. Ill 



In the long-styled form the stigmas project above the anthers, 

 and the styles are nearly twice as long as those of the short- 

 styled form, in which the stigmas stand beneath the anthers. 

 The stigmas in many, but not in all the short-styled flowers are 

 larger than those in the long-styled. The anthers of the short- 

 styled flowers stand on a level with the stigmas of the other 

 form ; but the stamens are longer by only one-fourth or one-fifth 

 of their own length than those of the long-styled. Consequently 

 the anthers of the latter do not stand on a level with, but rather 

 above the stigmas of the other form. Differently from what 

 occurs in the following closely allied genus, Sethia, the stamens 

 are of nearly equal length in the flowers of the same form. The 

 pollen-grains of the short-styled flowers, measured in their dry 

 state, are a little larger than those from the long-styled flowers 

 in about the ratio of 100 to 93.* 



SETHIA ACUMINATA (EKYTHROXYLHXE). 



Mr. Thwaites pointed out several years ago t that this plant 

 exists under two forms, which he designated as forma stylosa et 

 stamina i ; and the flowers sent to me by him are clearly hetero- 

 styled. In the long-styled form the pistil is nearly twice as 

 long, and the stamens half as long as the corresponding organs 

 in the short-styled form. The stigmas of the long-styled seem 

 rather smaller than those of the short-styled. All the stamens 

 in the short-styled flowers are of nearly equal length, whereas 

 in long-styled they differ in length, being alternately a little 

 longer and shorter; and this difference in the stamens of the 

 two forms is probably related, as we shall hereafter see in 

 the case of the short-styled flowers of Lythram salicaria, to the 

 manner in which insects can best transport pollen from the 

 long-styled flowers to the stigmas of the short-styled. The 

 pollen-grains from the short-styled flowers, though variable in 

 size, are to those of the long-styled, as far as I could make out, 

 as 100 to 83 in their longer diameter. Sethia obtusifolia is 

 heterustyled like S. ucuminata. 



* F. Miiller remarks iu his let- numbers; but the sepals and petals 



ter to me that the flowers, of which often vary from 5 to 7; tlio ot.i- 



he carefully examined many ape- metis from 10 to li, and the pistils 



cimens, are curiously variable from 3 to 4. 



iu the number of their parts: t ' Enumeratio Planturutn Zoy 



5 sepals and petals, 10 stameus Innirc,' 18G4, p. 51. 

 fcua a piitils are the prevailing 



