There are only six stamens; these are somewhat graduated in length, and their anthers in the short-styled form stand a little above the stigma, but yet by no means equal in length the pistil of the long-styled form. In the latter the stamens are rather shorter than those in the other form. The six stamens alternate with the petals, and therefore correspond homologically with the longest stamens of L. salicaria and L. Graefferi.
Lythrum hyssopifolia.
This species is said by Vaucher, but I believe erroneously, to be dimorphic. I have examined dried flowers from twenty-two separate plants from various localities, sent to me by Mr. Hewett C. Watson, Professor Babington, and others. These were all essentially alike, so that the species cannot be heterostyled. The pistil varies somewhat in length, but when unusually long, the stamens are likewise generally long; in the bud the stamens are short; and Vaucher was perhaps thus deceived. There are from six to nine stamens, graduated in length. The three stamens, which vary in being either present or absent, correspond with the six shorter stamens of L. salicaria and with the six which are always absent in L. thymifolia. The stigma is included within the calyx, and stands in the midst of the anthers, and would generally be fertilised by them; but as the stigma and anthers are upturned, and as, according to Vaucher, there is a passage left in the upper side of the flower to the nectary, there can hardly be a doubt that the flowers are visited by insects, and would occasionally be cross-fertilised by them, as surely as the flowers of the short-styled L. salicaria, the pistil of which and the corresponding stamens in the other two forms closely resemble those of L. hyssopifolia. According to Vaucher and Lecoq, this species, which is an annual, generally grows almost solitarily (4/9. 'Geograph. Bot. de l'Europe' tome 6 1857 page 157.), whereas the three preceding species are social; and this fact alone would almost have convinced me that L. hyssopifolia was not heterostyled, as such plants cannot habitually live isolated any better than one sex of a dioecious species.
We thus see that within this genus some species are heterostyled and trimorphic; one apparently heterostyled and dimorphic, and one homostyled.
Nesaea verticillata.
I raised a number of plants from seed sent me by Professor Asa Gray, and they presented three forms. These differed from one another in the proportional lengths of their organs of fructification and in all respects, in very nearly the same way as the three forms of Lythrum Graefferi. The green pollen-grains from the longest stamens, measured along their longer axis and not distended with water, were 13/7000 of an inch in length; those from the mid-length stamens 9 to 10/7000, and those from the shortest stamens 8 to 9/7000 of an inch. So that the largest pollen-grains are to the smallest in diameter as 100 to 65. This plant inhabits swampy ground in the United States. According to Fritz Muller, a species of this genus in St. Catharina, in Southern Brazil, is homostyled. (4/10. 'Botanische Zeitung' 1868 page 112.)
Lagerstroemia Indica.
This plant, a member of the Lythraceae, may perhaps be heterostyled, or may formerly have been so. It is remarkable from the extreme variability of its stamens. On a plant, growing in my hothouse, the flowers included from nineteen to twenty-nine short stamens with yellow pollen, which correspond in position with the shortest stamens of Lythrum; and from one to five (the latter number being the commonest) very long stamens, with thick flesh-coloured filaments and green pollen, corresponding in position with the longest stamens of Lythrum. In one flower, two of the long stamens produced green, while a third produced yellow pollen, although the filaments of all three were thick and flesh- coloured. In an anther of another flower, one cell contained green and the other yellow pollen. The green and yellow pollen-grains from the stamens of different length are of the same size.