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 prothallium, and forms its median line. The 

 anterior side projects above the back, and, where it meets the two posterior 



Fig. 312. — Development of the archegonia of 

 Salvinia natans (after Pringsheim, X 150). 



Fig. 313. — Salvinia natans ; median longitudinal section through the prothallium and young embryo ; y4 after the first 

 three divisions of the oospore, / and // are separated by the basal wall ; / the hypobasal segment divided by the wall jc into 

 the cells a and *; // 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, s apical cell of the scutiform leaf. III— VI the succeeding segments, 

 V apical cell of the stem ; mm 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 its 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) 



