CHAP. TV. POXTEDEIUA. 185 



tends towards violet, and no other such case is known. 

 Lastly, the three longer stamens alternate with the 

 three shorter ones, whereas in Lythrum and Oxalis 

 the long and short stamens belong to distinct whorls. 

 With respect to the absence of the mid-styled form in 

 the case of the Pontederia which grows wild in Southern 

 Brazil, this would probably follow if only two forms 

 had been originally introduced there ; for, as we shall 

 hereafter see from the observations of Hildebrand, 

 Fritz Miiller and myself, when one form of Oxalis is 

 fertilised exclusively by either of the other two forms, 

 the offspring generally belong to the two parent- 

 forms. 



Fritz Miiller has recently discovered, as he informs 

 me, a third species of Pontederia, with all three forms 

 growing together in pools in the interior of S. Brazil ; 

 so that no shadow of doubt can any longer remain 

 about this genus including trimorphic species. He 

 sent me dried flowers of all three forms. In the long- 

 styled form the stigma stands a little above the tips of 

 the petals, and on a level with the anthers of the 

 longest stamens in the other two forms. The pistil is 

 in length to that of the mid-styled as 100 to 56, and 

 to that of the short-styled as 100 to 16. Its summit is 

 rectangularly bent upwards, and the stigma is rather 

 broader than that of the mid-styled, and broader in 

 about the ratio of 7 to 4 than that of the short-styled. 

 In the mid-styled form, the stigma is placed rather 

 above the middle of the corolla, and nearly on a level 

 with the mid-length stamens in the other two forms ; 

 its summit is a little bent upwards. In the short- 

 styled form the pistil is, as we have seen, very short, 

 and differs from that in the other two forms in being 

 straight. It stands rather beneath the level of the 

 anthers of the shortest stamens in the long-styled and 



