FI Lie IN Em. 
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 ruptm-ed 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, 
fertiHsation 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 Equisetaceee, 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 testas, 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 Pteris 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. Salviniaeeaa. Plants floating horizontally on the surface of water. The 
sporocarp 
Fig. 2,2'^.— Marsilia Salvairix, 
(natural size), st the upper part of its pedicel; B a 
sporocarp which has burst in water and is protruding 
its gelatinous ring {after Haustein) ; C the gelatinous 
ring z ruptured and extended, sr compartments of 
the sporocarp ; sch testa of the sporocarp ; D a com- 
partment of an unripe sporocarp witfi itb sporangia ; 
E one from a ripe sporocarp ; microspcrangia, 
ma macrosporaiigia. 
^ [For further details on this subject see De Bary, Vergleichende Anatomie der Vegetations- 
organe, 1877.] 
