140 Transactions of the Society. 



to insure a supply of moisture, and there undergo a period of 

 maturation, after which free-swimming bodies are liberated. These, 

 therefore, do not correspond to the pollen of other plants, but to 

 the special fertilising cell. The possibility of this was long ago 

 foreshadowed by Hofmeister and by Pringsheim. 



This remarkable fact was first discovered by Hirase * in Salis- 

 buria, confirmed by Ikenof in Cycas (fig. 21), and by Webber X 

 in Zamia (fig. 22). 



The antherozoids of the Ginkgo are egg-shaped, those of Zamia 

 are pear-shaped, with a spiral ciliated band. 



Monocotyledons. 



HvDROOHARiDEiE. — The species of this order are aquatic, mostly 

 submerged, and in some cases marine, occurring on the shores 

 of the| Indian and Pacific Oceans, and of the West Indian islands. 

 There are fourteen genera, and about forty species. 



The flowers are produced singly, or several together in spathes, 

 which raise themselves above the water, when the flowers are about 

 to open. 



The ovary is inferior, 1-celled, with three parietal placentas, 

 or divided, sometimes into as many as nine cells. The fruit, which 

 is small and indehiscent, ripens under water. The seeds are few or 

 many. They are generally small, covered with filaments or spiny 

 in Limnobium, rugose or spiny in Thalassia. There is no albumen. 

 We have two native genera, each with one species. 



, Hydrocharis Morsus-ranx , the Frogbit, is a floating plant ; the 

 perianth has three outer segments, which are pale green, shorter 

 and narrower than the inner ones, which are white. 



The fruit is fleshy, small, ovoid or narrowed at the base in 

 its early stages, and strongly 6-ribbed, indicating the six carpels 

 of which it is composed. The ovules are numerous and inserted on 

 the septa, but only a few develop into seeds, which are small, ovoid, 

 and imbedded in a jelly-like mucus or pulp. These are not 

 naturally liberated until the decay of the fruit, which, however, is 

 no doubt often attacked by birds and other animals, which thus 

 effect the distribution of the seeds. 



The plant, like many other aquatic species, also multiplies by 



, * Hirase, S., "On the Spermatozoid of Giyikgo biloba." Bot. Mag. Tokio, x.(1896). 

 " Etud. s.l. fecondation et l'Embryogenie du Ginkgo biloba." Journ. Coll. Sci. Imp. 

 Univ. Japan, 1895. 



t Ikeno, S., " Unt. u.d. Entw. d. Geschlechts organ bei Cycas revoluta." Journ. 

 Coll. Sci. Imp. Univ. Japan, 1890. See also Jahr. f. Wiss. Bot., xxxii. heft 4 

 (Leipzig, 1898). 



X Webber, H. J., " Spermatogenesis of Zamia and the Pollen-tube App. of 

 Ginkgo." U.S. Dep. of Agric. Washington, 1901. " Div. of the Antherozoids of 

 Zamia." Bot. Gaz. Chicago, 1897. 



