Tebrtjaby 18, 1916] 



SCIENCE 



245 



hemisphere; the smaller particularly has been 

 collected at only a few stations in the West 

 Indies. 



The larger and more widely distributed is 

 Halophila Engelmanii Aschers. It is a del- 

 icate plant creeping over the muddy bottom 

 and rooting at the nodes by white fibrous roots. 

 The leaves are very short petioled, serrate and 

 produced in whorls or clusters, so accurately 

 described by Bailey Balfour^ for K. stipulacea 

 (Forsk.) Aschers., which he found on the island 

 of Eodriguez in 1874. The plants are dicecious 

 with axillary inflorescence. Small,^ who has 

 collected the species in the Florida Key region, 

 says the flowers and fruit have not been seen; 

 however, the author collected pistillate flowers 

 and ripe fruits in abundance in all the dredges 

 in which the plant came up. The flowers are 

 invested in a bibracteate axillary spathe on a 

 short pedicel. The original description of the 

 species by Ascherson^ is rather vague as to 

 the flowers since he classified the species largely 

 by the leaves and Bentham and Hooker* give 

 the species a casual and somewhat doubtful 

 treatment. A great many of the older writers 

 on the genus in describing the flowers of Halo- 

 phila mistook the pistil with the hypanthium 

 to be all pistil, and what are the true styles to 

 be long stigmas, thus completely overlooking 

 the perianth. The pistillate flower really con- 

 sists of a small flask-shaped ovary, sessile in 

 the spathe formed by the two bracts and pro- 

 longed into an elongated hypanthium, 3 mm. 

 in length, on top of which is the three-parted 

 perianth. This species, although it has not 

 been figured in any works so far as the writer's 

 knowledge goes, does not difl^er materially from 

 H. stipulacea (Forsk.) Aschers., found in the 

 Indian Ocean and described with such elab- 

 orate and careful drawings by Balfour,^ except 



1 Balfour, B., ' ' On the Genus Ealophila, ' ' 

 Trans. Bot. Soc, Edinburgh, XII., pp. 290-334, 

 1879. 



2 Small, J. K., ' ' Flora of the Florida Keys, ' ' 

 New York, 1913, p. 5. 



3 Ascherson, P., ' ' Neumayer Anleit. zu Wissen. 

 Beobacht. auf Beisen," 1857, p. 368. 



* Bentham & Hooker, "Genera Plantarum, " f. 

 III., p. 435. 



that the stipular bracts at the nodes are lack- 

 ing. 



H. Baillonis Aschers., the other and smaller 

 species found in the dredging operations, is the 

 only one in the genus that is monecious. Early 

 ^vriters suspected the monecism of this species, 

 but Holm's' work on the species confirmed the 

 suspicion. Holm's work also has been very 

 careful and accurate, but his plates do not 

 show the peculiar arrangement of the stami- 

 nate and pistillate flowers lying in such close 

 proximity in the spathe as to suggest self- 

 fertilization. Close pollination, however, does 

 not seem to be of general occurrence in the 

 genus. In appearance H. Baillonis Aschers. 

 resembles very much H. ovalis (R. Br.) J. D. 

 Hook, which is the most widely distributed 

 species in the genus occurring throughout the 

 Indian Ocean and South Sea, except that H. 

 Baillonis is monecious and has serrated leaves. 



The fertilization of Halophila has never 

 been actually seen, but the researches of both 

 Balfour and Holm on the morphology of the 

 anther and pollen have led to the supposition 

 that the manner of fertilization is similar to 

 that of Zostera marina as observed by Clavaud'' 

 and Engler^ except that in the latter plant the 

 pollen grains individually are elongated cylin- 

 drical bodies, while the pollen of Halophila oc- 

 curs in the anther sacs in coiled, spiral chains, 

 the pollen grains adhering to each other by a 

 mucilaginous substance. These chains are car- 

 ried from the proterandrous staminate flow- 

 ers to the long filiform styles of the pistillate 

 flowers in other spathes by the water current, 

 the chains getting entangled on these styles 

 and fertilizing the ovules. 



However interesting the structure of these 

 lowly submerged plants may be, the peculiar 

 conditions under which they were found grow- 



5 Balfour, loc. cit. 



6 Holm, Th., "Reoherehes anatomiques et morph- 

 ologiques sur deux Monoeotyledones Submerged," 

 Bihang. till. K. Svenska. Vet.- ATcad. Randlingar, 

 Bd. 9, No. 13, 1885. 



7 Clavaud, Armand, ' ' Sur le veritable mode de 

 Fecondation du Zostera marina," Ann. Soc. Linn. 

 Bordeaux, p. 109, 1878. 



e Engler, A., Botan. Zeit., p. 654, 1879. 



