MARGINARIA. 



[ 415 ] 



MARSILEACE.E. 



found crystallized within the cells of fatty 

 tissue (PI. 7. fig. 15 a). 



BIBL. That of CHEMISTRY. 



MARGINARIA, Bory. A genus of Po- 

 ly podieae (Ferns), with the naked sori im- 

 bedded deeply in the backs of the veins and 

 venules. The sporanges are borne on long 

 pedicels, and are intermixed with articulated 

 paraphyses. 



MARGINULINA, Ehr. A genus of Fo- 



RAMINIFERA (p. 270). 



MARSILEA, L. A genus of Marsileacese 

 (Flowerless Plants), growing in mud, by a 

 creeping rhizome, from which arise erect 

 filiform leaf-stalks, supporting a compound 

 four-lobed blade ; at the bases of the leaf- 

 stalks arise also stalked capsules, chambered 

 in the interior, being divided by one perpen- 

 dicular and many horizontal septa ; in these 

 chambers are found sacs (sporanges) con- 

 taining the spores. The spores are of two 

 kinds, the larger representing ovules, the 

 smaller pollen ; but while the former pro- 

 duce a single archegone in germination, like 

 those ofPilularia, the pollen-spores produce 

 numerous vesicles in their interior, which 

 become the parent-cells of sperinatozoids. 

 The capsules of Marsilea have a regular de- 

 hiscence when ripe, and the whole mass of 

 the spore-sacs is extruded on a thick gela- 

 tinous stalk-like process, produced from the 

 interior. As these plants do not occur in 

 this country, we do not enter very minutely 

 into their characters, especially as in all 

 essential respects they agree with PILU- 



LARIA. 



BIBL. See MARSILEACEJE. 



MARSILEACE.E. A family of Flower- 

 less plants possessing a distinct leafy stem, 

 composed of a small number of plants, of 

 minute dimensions, but of great interest in 

 a physiological point of view. They are all 

 aquatics, some growing in the mud in and 

 around ponds, others floating on the surface 

 of stagnant waters. Known perhaps only to 

 the botanist, they are distinguished from the 

 families to which their reproductive structures 

 ally them most closely, by the much more 

 perfect separation of these from the vegeta- 

 tive structure. They all bear distinct spore- 

 fruits or sporocarps, seated on a stalk arising 

 from the stem. These contain sporanges or 

 spore-sacs, differently arranged in the dif- 

 ferent genera, but agreeing in this respect, 

 that they contain spores of two kinds, ana- 

 logous to the two kinds of spore in Lyco- 

 podiacese, but differing in their mode of 

 development. 



Pilularia globulifera is the only British 

 representative of this family ; a description 

 of its organization is given under the head 

 of PILULARIA. It agrees with Marsilea, a 

 genus occurring on the continent, in possess- 

 ing only one kind of sporocarp, which con- 

 tains spore-sacs, part of which contain ovu- 

 lary spores, part pollen-spores ; the principal 

 difference being that the sporocarps are of 

 more complex structure in Marsilea. Sal- 

 vinia, consisting of floating aquatic plants, 

 possesses two kinds of sporocarp, which may 

 be called male and female, and the same is 

 the case with Azolla ; the development of 

 the plants of the last genus, however, has 

 not yet been thoroughly elucidated. 



The principal characteristics, in which all 

 these plants agree, consist in the possession 

 of free stalked sporocarps, quite distinct from 

 the leaves, and the production of two kinds 

 of spore, which agree in the history of de- 

 velopment. The small spores produce sper- 

 matozoids, formed in vesicles developed in 

 chambers into which the spores become di- 

 vided in germination. The large spores, 

 which are more highly organized than those 

 of LYCOPODIACE^E, produce in germination 

 a prothallium, somewhat like that of Lyco- 

 podiacese, inside the outer coat of the spore, 

 on which is developed a single archegonium 

 in Pilularia and Marsilea, several archegonia 

 in Salvinia. The conditions in Azolla at 

 this stage are unknown. The germ-cell of 

 the archegonium, fertilized apparently by 

 the spermatozoids, becomes developed in 

 situ into the new leafy plant, which was 

 thus formerly regarded as a product of the 

 simple germination of the spore. More de- 

 tailed particulars are given under the heads 

 of the genera. The distinctive characters of 

 the genera may be given as follows : 



Genera. 



* Stems creeping over mud, rooting ; sporo- 

 carps of one kind, containing spore-sacs 

 of each kind. 



I. Pilularia. Leaves filiform. Sporocarps 

 globular, almost sessile, four-celled, contain- 

 ing the two kinds of spores in distinct sacs. 



II. Marsilea. Leaves cruciately four- 

 lobed; lobes obcordate. Sporocarps stalked, 

 two-celled, the two cells divided transversely 

 into many smaller cells. 



** Plants floating like Duckweed; sporo- 

 carps of two kinds. 



III. Salvinia. Leaves opposite, small, 

 glandular, floating. Sporocarps on sub- 



