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MEMOIRS OF THE NEW YORK BOTANICAL GARDEN [Vol. 9, No. 2 



some species of the subgenus Lophotocarpus. These perfect flowers are signalized 

 by a ring of more or less functional stamens in an otherwise pistillate flower. The 

 appearance of functional pistils in staminate flowers has never been reported 

 although aborted pistils appear sporadically in the staminate flowers of several 

 species. Flowers are produced throughout the growing season. 



The three sepals are herbaceous and persistent. They are often characteristi- 

 cally adorned with papillosities, pubescence, and striae. Those of the staminate 

 flower are reflexed, while those of the pistillate flower are reflexed in the sub- 

 genus Sagittarie (fig. 17d) and spreading or appressed in the subgenus Lophoto- 

 carpus (fig. 2e). 



The three white or rarely pink petals are deciduous and occasionally have a 

 purple spot at their base. They are often quite showy, averaging about twice the 

 size of the sepals. In several species flowers are double through the replacement 

 of stamens by additional petals (S. latifolia, S. sagitti folia). 



The whorled stamens vary from seven to numerous. Their filaments are im- 

 portant diagnostically in shape, size, and indument. They may be either linear, 

 subulate, or dilated, and glabrous or pubescent. The bilocular, basifixed anthers 

 vary in shape from linear to nearly orbicular. The pollen grains are yellow, nearly 

 spherical, ca. .02 mm in diameter with somewhat pitted walls (Buchenau 1903, 

 p. 7). The numerous pistils are free, hypogynous, 1-celled, 1-ovuled, and spirally 

 arranged on a dome-shaped receptacle. Each has a terminal style that varies 

 remarkably little throughout the genus and proves quite useless in specific deter- 

 mination. The ovules are anatropous. Pollination is accomplished largely by in- 

 sects attracted by the ephemeral petals, although foraging snails probably play a 

 small part, at least in some species. 



Fruit. Each pistil matures into a most characteristic achene which furnishes 

 the surest means of specific identification. Among the diagnostic characters to be 

 sought are the size, shape, and insertion of the achene-beak; the size, number, 

 and shape of the facial wings, if present; the presence or absence of resin-ducts; 

 the size and shape of the dorsal wings; and the general shape and size of the 

 achene itself. Externally all have a fine cellular-reticulate appearance that is 

 insensibly lost at or near maturity. The seed is without endosperm; the embryo is 

 horseshoe-shaped. The achenes are retained on the receptacle until maturity and 

 are then water-dispersed. The resin-ducts and various wings of the achenes are 

 reported to be a buoyancy factor in water-dispersal (Buchenau 1903, p. 8). 



It should be noted that all descriptions and measurements used in this paper 

 are based on dried specimens, except for the stamens, which were restored by 

 boiling. 



CYTOLOGY 



The literature has scattered references to chromosome counts of the genus. 

 The most comprehensive lists are those of Brown (1947) and Delay (1951). A 

 table of taxa follows with their reported chromosome numbers and the earliest 

 authority for each. Using the abundant fresh material available in the New York 

 area and fixed material from more remote places, the writer was able to verify 

 these counts in most of the species he examined. The counts verified or deter- 

 mined by the writer are marked with an asterisk. Anther smears stained with 

 propionocarmine were used to determine the haploid number, while squashes of 

 young, active root-tips, similarly stained, were the source of the diploid number. 



