Farmer — On the Structure of a Hybrid Fern . 537 
the rest for our present purpose, and they will not be 
further considered here. 
Turning now to the sporangia, I have already alluded to 
the dimorphic character of the leaves in both P. eleg antis- 
sinrnni and P. Schneider i . In the former Fern the sori are 
found far more abundantly on the plain than on the dis- 
sected fronds, and, when plain pinnae occur on a dissected 
frond, the sori are far more abundant on the uncut portions 
(PL XXIV, Fig. 15 a) ; still the sporangia of both leaf-forms 
produce germinable spores, and indeed it was from spores 
of these dissected leaves that the parent prothallia were 
grown. In the case of P. Schneideri , however, it is rare to 
find sporangia upon the dissected leaf at all, and when they 
do occur they are quite barren. Mr. Schneider tells me he 
has never succeeded in raising any prothallia from them, 
and his statement is borne out by the fact that in all the 
specimens I was able to examine I found the spores de- 
generated. The abortion frequently does not become apparent 
until the spore-mother-cell, or even the tetrad, stage is 
reached ; but in any case the mature sporangium only con- 
tains a granular mass resembling a heap of angular composite 
starch-grains. 
In marked contrast to the scarcity of sporangia on the normal 
fronds of P. Schneideri stands their extreme abundance on the 
reverted leaves ; even any odd pinna of a normal frond which 
exhibits a plain instead of a cut outline is commonly crowded 
with sori (PL XXIV, Fig. 18). And yet it is quite certain 
that the majority at any rate of these sporangia are sterile. 
Some appear, notwithstanding, to possess good spores, but 
they have not yet been successfully germinated. Mere 
appearance, however, forms but an unsafe guide in estimating 
germinating power, as is proved by the case of Adiantum 
Farley ense . This Fern is, on good grounds, believed to have 
arisen as a sport from A. tenerum in Barbados, and although 
it sometimes bears sporangia containing spores which are 
to all appearance good, they are said, by the best authorities 
competent to judge, to be incapable of germination. It is 
