Hydrales.] 



ZOSTER ACE^, 



145 



Order XLI. ZOSTERACEiE.— Sea wracks. 



Zosteimx.—Necs ab Esenb.exKvinth.—Zostetex.—Kunth.emuH. 3. 115.(1841).— Posidonie8c.-/d. 



Diagnosis. — Hydral Endogem with hypogynom stamens^ a free ovary, and confervoid pollen. 



Marine plants resembling sea weeds and living among them. Leaves grassy, thin, 

 sheathing at the base. Flowers very minute, absolutely naked, 

 or smTounded by 3 scales, $ $ , arranged within herbaceous 

 spathes. $ Anthers definite in number, one or two-celled, 

 sessile ; pollen filamentous, resembluig fine confervse. ^ Ovary 

 free, one-celled ; ONOile sohtai-y, pendulous, campylotropal ; or 

 parietal ^^'ith the foramen do\Miwards ; stigmas 1 or 2, capillary. 

 Fruit di'upaceous, one-seeded. Seed pendulous ; albumen ; 

 embryo antitropal or homotropal, wdth a very large radicle, and 

 a highly developed plumule l^Tng in its cavity. 



If we are to find anywhere a positive intercalation of flowei'mg 

 with flowerless plants it is here, where with naked flowers, but 

 distinct sexes, we have the pollen in a condition that may be well 

 compared to the elaters of Marchantia and its alKes, and totally i 

 different from all that is kno\\Ti in other flowei^ing plants. 

 The habit too is quite that of sea weeds. It therefore seems 

 expedient to separate these genera from the Naiads, which are 

 an Order higher m organization, and in fact differ in nothing 

 from the common t}-pes of flowering structure, except in their 

 simphcity. The mamier in which fertilization takes place among 

 these plants is unknown. Zostera marina, whose flowers of both 

 sexes are inclosed in a spathe filled with air, offers indeed no 

 insuperable difficulty to the supposition that in such a situation, 

 although the plants are mider water, }'et the flowers may be 

 in a dry medium ; but, as Vaucher has observed, this does not ^ 

 assist u3 to understand how fertilization is effected in Zostera 

 maritima which is dioecious. Does the confervoid pollen float to 

 the place where it is wanted ? 



The bottom of the ocean is the locahty of these plants, which 

 occur from the North Sea to the Mediterranean, the Indian Ocean ' 

 and the coasts of Arabia. One species indeed, Amphibolis 

 zosteraefoha, is seen on the shores of New Holland, and another 

 in the West Indies. 5 



They can scarcely be said to form any part of the vegetation 

 subdued by man, except hi the case of the Sea wrack, Zostera 

 marina, which is a common material for packing, and for stuffing 

 cottagers' cushions, and has also been used for tumours, owing 

 apparently to the iodine of the sea weeds that are gathered 

 with it. 



Cymodocea, Knnig. 

 Amphibolis, Agh. 

 Graiimullera, Rchb. 



GENERA. 



Thalassia, Sol. 

 Zostera, L. 



m 



Posidonia, Kiin. 

 Kcrnera, W. 

 Caulinia, DC. 



Numbers. Gen. 5. Sp. 12 (Kunth). 



Position. 



CeramiacecB. 

 -. — Zosterace^. — Naiadaceae. 

 Marchan tiacecB. 



Fig.XCV. 



Fig. XCV.— Zostera Noltii. 1. An anther; 2. a portion of a spathe opened, to show the 9 and 5' 

 flowers ; 3. a section of the ovary ; 4. a seed; 5. the same cut in half, to show the plumule ; 6. an 

 anther opened and discharging its confervoid pollen. — Nees v. Esenbeck. 



L 



