FILICINEm. 
445 
arches convexly, and the prothallium is thus pushed further outwards. This 
is the present state of our knowledge with respect to the position of the prothallium 
in the macrospore. (Compare the explanations of the figures further on.) 
The prothallium of Salvinia natans attains a much more considerable size than 
that of the two other genera already mentioned ; it contains abundance of chlo- 
rophyll, and forms a number (which may even be large) of archegonia in definite 
positions. After it has broken through the membrane of the papilla, it appears, 
seen from above, as three-sided between the three torn lobes of the epispore ; 
one of these sides is anterior ; the two posterior sides meet behind at an acute 
angle; a line from this angle to the centre of the anterior side runs above the 
elevated saddle-shaped back of the prothalhum, and forms its median line. The 
anterior side projects above the back, and, where it meets the two posterior 
Fig. -^t.-?,.-— Salvinia nataiis ; median longitudinal section through the prothallium and young- embryo ; A after the first 
three divisions of the oospore, / and // are separated by the basal wall ; / the hypobasal segment divided by the wall into 
the cells a and b ; II the epibasal segment, divided by the wall 2 (transverse wall) ; cd axis of growth ; B embryo in a further 
stage of development, rrr first stage of the foot, J apical cell of the scutiform leaf, /// — VI the succeeding segments, 
V apical cell of the stem ; in in A and B the closing cells of the archegonium (after Pringsheim). 
sides, the two angles grow subsequently into long wing-like prolongations 
hanging down by the sides of the macrospore. The first archegonium makes 
its appearance on the median line of the elevated back immediately behind the 
growing anterior side of the prothallium ; two other archegonia then invariably 
appear right and left of the first, so that they stand in a transverse row parallel 
to the anterior side. If one of these archegonia is fertilised there is an end of 
the growth of the prothallium; but if this does not happen, the prothallium continues 
to grow on it^ anterior side, and from i to 3 new transverse rows of archegonia 
are produced, each of which contains from 3 to 7. The long oosphere of each 
archegonium lies obliquely in the tissue of the prothallium, so that the outer (neck) 
