CHAP. III. 
FERNS. 
261 
mature, continue covered with the superincumbent portion 
of the epidermis, which is then called the indusium or hivo- 
lucrum (memhranula, Necker ; glandules squamoscB, Guettard). 
In Trichomanes andHymenophyllum, the sporangia are seated 
within the dilated cup-like extremities of the lobes of the 
frond, and are attached to the vein which passes through 
their axis, which is then called their receptacle. In Gleicheni- 
aceae, the sporangia have a transverse complete, instead of a 
vertical incomplete, ring, and they are nearly destitute of 
stalks ; in others the sori occupy the whole of the under sur- 
face of the leaf, which becomes contracted, and wholly alters 
its appearance : the sporangia have no ring, and the cellular 
tissue of their membrane is not reticulated, but radiates 
regularly from the apex. 
In these plants it has been in vain endeavoured to discover 
traces of organs of fecundation. Nevertheless, as it was diffi- 
cult for sexualists to believe that plants of so large a size 
were destitute of such organs, it has been considered indis- 
pensable that they should be found ; and, accordingly, while 
all seem to agree in considering the sporangia as female 
organs, a variety of other parts have been dignified by the 
title of male organs : thus, Micheli and Hedwig found the 
latter in certain stipitate glands of the leaf ; Staehelin, Hill, 
and Schmidel, in the elastic ring ; Koelreuter, in the indusium ; 
Gleichen, in the stomates; and Von Martins, in certain 
membranes enclosing the spiral vessels. None of these 
opinions are now adopted. M. Bory de St. Vincent contends 
that impregnation may take place in plants without the 
agency of pollen, and he affirms that hybrid ferns exist; 
which, if true, would render it impossible to deny the exist- 
ence, in this large order, of sexual organs; but where are 
they? [Comptes Rendus^ v. 125.) 
In Ophioglossacem, a remarkable tribe of Ferns, the fertile 
leaf is rolled up in two lines parallel with its axis or midrib, 
and at maturity opens regularly by transverse valves along 
its whole length, emitting a fine powder, which, when magni- 
fied, is found to consist of particles of the same nature as the 
spores found in the sporangia of other ferns ; here there are 
no sporangia, the metamorphosed leaf probably performing 
s :3 
