422 
VASCULAR CRYPTOGAMS. 
cell remains undivided. The cells develope into germinating filaments, bursting the 
exospore in three directions ; these filaments then grow at their apex, and become 
segmented by septa ; only one of them however generally attains a more decided 
development, the others soon assuming the form of hairs. In Hymenophyllum Tun- 
hridgense this one frequently developes at once into a cellular plate ; but in other 
species it forms a much-branched conferva-like protonema, on which flat prothallia 
2 to 6 lines in length and ^ to li in breadth are formed as lateral shoots. Each cell 
of the filament may give rise to a branch which is given off behind the anterior 
septum, and is at once separated by another septum. Some of these branches 
continue to grow indefinitely like the mother-shoot, others end in becoming hairs ; 
a larger number are transformed into flat prothallia, but most develope into 
root-hairs. Here and there the rudiment of a filamentous branch becomes con- 
verted into an antheridium, or even into an archegonium. At the apex of the 
flat prothallia spherical cells arise in Trichomanes i7icisu7n on marginal flask-shaped 
cells : these must probably be considered as organs of propagation ; but the mar- 
ginal cells of the flat prothallia may develope into root-hairs and new protonemal 
filaments, and also into new flat shoots. The root-hairs are mostly short, with 
brown walls, and produce at their end lobed attaching-discs or branching tubes. 
In the Polypodiaceae and Schizaeaceae the endospore developes into a short 
articulated filamentous protonema, at the end of which, even at an early stage, a 
more or less considerable increase in breadth takes place ; a plate of tissue is thus 
formed consisting at first of only one layer, which soon assumes a broadly cordate 
or even reniform shape, and has its growing apex situated in an anterior depression. 
Its apical cell forms two rows of segments right and left, by walls which are per- 
pendicular to the surface, and from their further divisions the flat tissue is produced. 
The power of rejuvenescence of the apical cell is, however, limited ; it ends in 
the formation of a septum by which a new apical cell is formed, which then divides 
by longitudinal walls, and thus forms a row of apical cells lying side by side 
which occupies the bottom of the depression of the prothallium-disc, in the same 
manner as in the thallus of Pellia. The root-hairs are all lateral structures, 
springing in large numbers from the under-side of the posterior part of the pro- 
thallium; among them are the antheridia, which in this case are only rarely 
marginal. The archegonia are also produced on the under-side, but on a cushion 
behind the anterior depression formed of several layers; in Ceratopteris several 
cushions are formed bearing archegonia. 
Osmunda (examined minutely by Kny, and compared with the preceding, /. <:.) 
is distinguished in the first place from the Polypodiaceae and Schizseaceae by the 
absence of the protonematous filament. The endospore undergoes divisions at the 
very commencement of germination, which form a plate of tissue of which a pos- 
terior cell is converted, as in Equisetaceae, into the first root-hair. The succeeding 
root-hairs arise from marginal cells and on the- under-side of superficial cells of the 
prothallium, the apical growth of which follows a similar course to that of Polypo- 
diaceae. The mid-rib consisting of several layers is characteristic of Osmunda, 
penetrating the ribbon-like prothallium from the posterior end to the apex, and 
producing a large number of archegonia on both sides. The antheridia spring partly 
from the margin, partly from the lower surface with the exception of the mid-rib. 
