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Show 184 HETEROSTYLED TRIMORPHIC PLANTS. CuAP. IV. with water from the longer stamens of the short-styled form are to those from the shorter stamens of the S<-tlne fonn as 100 to 87 in diameter, as deduced from ten measurements of each kind. We thus see that the organs in these two fonns differ from one another and are an~anged in an analogous manner, as in the long and short-sty led forms of the tl'"imorphic species of Lythrum and Oxalis. Moreover, the longer stain ens of the long-sty led form of Pontederia, and the shorter ones of the short-sty led form are placed in a proper position for fertilising the stig1na of a mid-styled form. But Fritz MUller, although he examined a vast nu1nbor of plants, could never find one belonging to the midsty led form. The older flowers of the long-sty led and short-styled plants had set plenty of apparently good fruit; and this might have been expected, as they could legitiinately fertilise one another. Although he could not :find the mid-sty led form of this species, he possessed plants of another species growing in his garden, and all these were Inid-sty led; and in this case the pollen-grains from the anthers of the longer stamens were to those from the shorter stamens of the same flower as 100 to 86 in diameter, as deduced from ten Ineasurements of each kind. Those 1nid-styled .Plants growing by themselves never produced a single fruit. Considering these several facts, there can ha.rdl y be a doubt that both these species of Pontederia are heterosty led and trimorphic. This case is an interesting one, for no other Monocotyledonous plant is known to be heterostyled. Moreover, the flowers are in·egula.r, and all other heterostyled plants have almost symmetrical flowers. The two forms differ somewhat in the colour of their corollas, that of the short-styled being of a darker blue, whilst that of the long-styled CHAP. IV. PONTEDERIA. 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. vVith 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 Muller and myself, when one for1n of 0xalis is fertilised exclusively by either of the other two forms, the offspring generally belong to the two parentforms. Fritz Muller has recently discovered, as he informs n1e, 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 longstyled 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 l;>roader than that of the mid-styled, and broader in about the ratio of 7 to 4 than that of the short-sty led. In the mid-styled form, the stigma is placed rather above the middle of the corolla, and nearly on a level with the mid-lengtli stamens in the other two forms; its summit is a little bent upwards. In the shortstyled 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 |
