Bower.—Studies in the Phytogeny of the Fi lie ales. VIII . 353 
face (right in Fig. 6). There is, however, a difference in outline, those of 
Loxsomopsis being more flattened, so that the annulus, though continuous as 
a complete ring, appears to form a margin to the almost discoid capsule. 
The degree of induration is limited in Loxsoma to some twenty cells or less at 
the side of the ring remote from the stalk, the rest making up about half of 
the ring not being indurated : in this they are reduced, and appear as 
a vestigial tract of the annulus. No distinct stomial group is seen in 
Loxsoma} In Loxsomopsis nearly three-quarters of the ring is indurated, 
and an obliquely lateral stomium is well defined. There are two ways in 
which the sporangium of Loxsoma may be interpreted in relation to that of 
Loxsomopsis on the one hand, and that of the Schizaeaceae on the other. 
The current interpretation is founded on the fact that the sporangium of 
Loxsoma appears to share with the Schizaeaceae and Gleicheniaceae the 
dehiscence in the median plane, and accordingly it is held to be in that respect 
relatively primitive. But the state now observed in Loxsomopsis suggests 
another possibility: viz. that Loxsoma itself may have been derived from a 
type with the features now seen in Loxsomopsis , and that its median dehiscence 
may have originated secondarily by rupture of the indurated distal portion 
of the annulus. That rupture actually occurs in the position which would 
be most convenient for the shedding of the spores in a sporangium in which half 
of the annulus is mechanically ineffective. The facts appear insufficient to 
form a basis for a settled opinion oh this point: if the latter view be found 
correct, one of the most interesting points of Loxsoma for comparison with 
the Simplices which have median dehiscence would fall away. 
Such considerations leave still unresolved the difficulty of transition 
from the types of sporangium with complete annulus and median dehiscence, 
as seen in the Gleicheniaceae and Schizaeaceae, to those which also have an 
oblique annulus, but lateral dehiscence. The biological advantage of the 
change is patent in any crowded sorus. The sporangial type of Gleichenia 
or Schizaea demands elbow-room laterally for effective shedding of the 
spores : room which could not be afforded where the parts are closely 
packed. The lateral dehiscence, whether by means of an oblique or a 
vertical annulus, allows of the distal part of the ring being everted and the 
spores being shed distally. This is the natural method for gradate and 
mixed sori. It may be held that in these the annulus is the correlative of 
the annulus in the higher Simplices. What we require is evidence of how the 
transition came about. It seems that the comparison of the Simplices on 
the one hand with Loxsoma , and on the other with I.oxsomopsis , does not 
even yet yield decisive evidence. But all that would be required to carry 
out the change would be the establishment of a region of imperfect indura¬ 
tion of the cells of the ring of a more perfect sort than that seen in the 
Simplices, and a swing of its position to one side or the other. 
1 Compare Ann. of Bot., vol. xxvii, Pl. XXXIV, Figs. 2 6 a, c. 
