114 HETEBOSTYLED DIMORPHIC PLANTS. CHAP. III. 



other species shows that P. Ust&rta is so strongly pro- 

 terandrous (the anthers generally falling off before the 

 stigmas are mature) that the flowers must be cross- 

 fertilised by the many insects which visit them. Other 

 species bear much less conspicuous flowers which se- 

 crete little or no nectar, and consequently are rarely 

 visited by insects ; these are adapted for self-fertilisa- 

 tion, though still capable of cross-fertilisation. Ac- 

 cording to Delpino, the Polygonaceae are generally 

 fertilised by the wind, instead of by insects as in the 

 present genus. 



LEUCOSMIA BURNETTIANA (THYMELUE). 



As Prof. Asa Gray has expressed his belief * that tliis species 

 and L. acuminatu, as well as some species in the allied genus 

 Drymispermum, are dimorphic or heterostyled, I procured 

 from Kew, through the kindness of Dr. Hooker, two dried 

 flowers of the former species, an inhabitant of the Friendly 

 Islands in the Pacific. The pistil of the long-styled form is to 

 that of the short-styled as 100 to 86 in length; the stigma 

 projects just above the throat of the corolla, and is surrounded 

 by five anthers, the tips of wliich reach up almost to its base ; 

 and lower down, within the tubular corolla, five other and 

 rather smaller anthers are seated. In the short-styled form, 

 the stigma stands some way down the tul>e of the corolla, nearly 

 on a level with the lower anthers of the other form : it differs 

 remarkably from the stigma of the long-styled form, in being 

 more papillose, and in being longer in the ratio of 100 to 50. 

 The anthers of the upper stamens in the short-styled form aro 

 supported on free filaments, and project above the throat of the 

 corolla, whilst the anthers of the lower stamens are seated in 

 the throat on a level with the iipp< r stamens of the other form. 

 The diametejs of a considerable number of grains from both sets 

 of anthers in both forms were measured, but they did not differ 

 in any trustworthy degree. The mean diameter of twenty-two 



* 'American Journal of Sci- * Journal of Botany,* vol. iii. 1865, 

 ence,' 18G5, p. 101, and Sieinann's p. :;05. 



