414 
VASCULAR CRYPTOGAMS. 
the middle of the lamina {0. pe7idulu?7i), or the two branches of the leaf appear as if 
separated deep down to their origin {0. Bergianum\ or, finally, the fertile branch 
springs from the middle of the leaf-stalk {Botrychium rutcßfolium and dissecium). 
The Sporangia of the Ophioglossaceae are so essentially different from those of 
Ferns and Rhizocarps that these plants cannot, for this reason, be arranged in 
either of these classes. They arise from several epidermal cells. The wall of the 
sporangium consists of several layers of cells, its outer limit being formed by the 
epidermis of the leaf itself. The mother-cells of the spores in Botrychium Lunaria 
and probably also in Ophioglossum are derived, according 
to Goebel {loc. cii), from a single central cell (archesporium) 
which is invested by peculiar cells (forming the tapetum) 
developed by the division of the surrounding ceils of the 
sporangium. A longitudinal section through the unripe 
so-called spike of 0. vulgatum (Fig. 290) shows that the 
outer layer of the wall of the sporangium is a continuous 
prolongation of the epidermis provided with stomata and 
covering the whole of the fertile branch of the leaf. At 
the places where the lateral transverse line of dehiscence 
subsequently appears in each sporangium, these epidermal 
cells are elongated radially, and the whole layer exhibits 
an indentation at first scarcely perceptible. The spherical 
cavities which contain the masses of spores are imbedded 
in the tissue of the organ, and are therefore entirely sur- 
rounded by its parenchyma, there being several layers of 
it on the outer side where the transverse fissure subsequently 
arises. The middle part of the mesophyll is penetrated by 
fibro-vascular bundles which anastomose with one another 
into long meshes, and send out a bundle transversely between 
each pair of sporangial cavities. The course of development 
is the same in Botrychium, if the separate sporangiferous 
branches of the panicle are compared with the spike of 
Ophioglossum. The sporangia are similarly placed on them 
in two rows and alternate ; only they project further because 
the tissue between each pair of sporangia is but slightly 
developed. Four spores are formed from each mother-cell. 
The mother-cell, after an indication of a division into two, 
divides into four segments, each surrounded by a delicate 
cell-wall. The protoplasm of each of these special mother- 
cells becomes invested by a new wall, the true wall of the spore, and the primary 
walls become absorbed, so that the spores become free. In specimens of both 
genera preserved in spirit, the young spores, still connected together in fours, are 
found imbedded in a colourless, granular, coagulated mass of jelly, which in the 
living plant clearly corresponds to the fluid in which the spores of other Vascular 
Cryptogams float before they are ripe. The spores are tetrahedral ; in Botry- 
chium they are provided, even in a very early state, with knob-Hke projections on 
the cuticularised exospore. 
FIG. 290.— Longitudinal section 
through the upper part of a spike 
of Ophioglossum vulgatum ; s 
its free apex, sj> the sporangial 
cavities, r the part where they 
burst transversely ; g the fibro- 
vascular bundles (X about lo). 
