FILICINE^. 



459 



containing the sori which are less capable of swelling-up. As the ring gradually 

 expands the attachments of the chambers to the dorsal margin of the sporocarp 

 become ruptured and they are drawn completely out of the testa. As a rule the 

 attachment of the ring is broken through at one end, it then straightens itself and 

 bears the chambers, which are still closed sacs, in two longitudinal rows, there being 

 now a considerable interval between each pair of chambers, whereas they were closely 

 packed together whilst still within the testa. These processes are completed in a few 

 hours, both kinds of spores are set free, and, if the temperature be favourable, 

 fertilisation takes place within from twelve to 

 eighteen hours after placing the sporocarp in 

 water. 



(a) Histology'^. The development of the tissues 

 of the Rhizocarps agrees in all essential points 

 with that of the true Ferns. The growth of the 

 stem, of the root, and to a certain extent of the 

 leaves, by means of an apical cell, is as evident 

 here as in the Characeae and Equisetaceae, and 

 has been thoroughly studied. The epidermis 

 presents several peculiarities, more especially as 

 to the stomata. The fundamental tissue is re- 

 markable, as is usually the case with water or 

 marsh plants, for its large intercellular spaces. 

 For information as to the occurrence of scleren- 

 chyma in the leaves and in the testae, the me- 

 moirs of Braun and of Russow must be consulted. 

 The fibrovascular bundles, more especially those 

 of the Marsiliaceae, very closely resemble those 

 of the true Ferns in their composition. There 

 is a central xylem entirely surrounded by phloem, 

 and this again is invested by a single layer of 

 cells with folded lateral walls forming the bundle- 

 sheath. A single bundle traverses stem, root, and 

 leaf. In Marsilia, the bundle branches in the leaf, 

 forming a dichotomous venation. A transverse 

 section of the stem of the Marsiliaceae shows the 

 fibrovascular mass forming a ring surrounding a 

 central mass of fundamental tissue. The fibro- 

 vascular mass consists evidently of several bundles 

 which have coalesced ; that this is so is indicated 

 by the fact that the phloem of its inner side is 

 bounded by a bundle-sheath just as the outer 



side is. In Pter'is aquilina it often happens that the two wide cauline bundles of the 

 stem unite laterally so as to form a tube enclosing a medulla. 



(b) Classification. It is already evident from what has been already said, that the 

 Rhizocarpeae belong to two clearly-defined families, of which the one, the Salviniaceae 

 is closely allied to the true Ferns, whereas in the other, the Marsiliaceae, the especial 

 characteristics of the order find their most complete expression. 



Family i. SalviniaeesB. Plants floating horizontally on the surface of water. The 



Fig. ^zi,.— Marsilia Salvatrix; A a sporocarp 

 (natural size), st the upper part of its pedicel; A' a 

 sporocarp which has burst in water and is protruding 

 its gelatinous ring (after Hanstein) ; C the gelatinous 

 ring .^ ruptured and extended, sr compartments of 

 the sporocarp ; sch testa of the sporocarp ; D a com- 

 partment of an unripe sporocarp with its sporangia ; 

 E one from a ripe sporocarp ; mi microsporangia, 

 ma macrosporangia. 



^ [For further details on this subject see De Bary, Vergleichende Anatomic der Vegetations- 

 organe, 1877.] 



