Notes . 
167 
After the first antheridium is formed the basal cell, from which the 
first antheridium mother-cell was cut off, may swell out laterally, and 
a second segment is then cut off and develops into an antheridium. 
Similarly a third antheridium may be formed from the basal segment. 
It need hardly be said that the main, though not the sole, biological 
interest which attaches to the present remarkable prothallium, centres 
round the question whether its structure is primitive or not. Two 
different interpretations may be placed on such a filamentous 
prothallium : — 
(1) It may be regarded as directly representing an algoid ancestor 
in the phylogeny of Schizaea and of Ferns generally ; 
(2) Or the filamentous structure may be considered to be a secon- 
dary adaptive character of no phylogenetic import. 
Goebel 1 has discussed the question with reference to the fila- 
mentous prothallium of Trichomanes, and has pointed out that it is 
not clear why, amongst the Hymenophyllaceae, the species of Tricho- 
manes should in general possess a filamentous prothallium, whilst 
those of Hymenophyllum are flattened cellular expansions, for they live 
under similar conditions. It is difficult to see, therefore, how the 
filamentous condition can be adaptive. The filmy character of the 
leaves of the Hymenophyllaceae may be an adaptive character, due 
to their moist environment. Species of other genera of Ferns, living 
under similar conditions, show corresponding adaptive modification 
of their leaves. But so far as is known their prothallia are never like 
those of Trichomanes , but resemble the prothallia of forms to which 
they are respectively related. 
If we now compare Trichomanes with Schizaea bifida we find that 
the latter lives under conditions which are quite distinct from those 
necessary for Trichomanes . We can hardly suppose that it is moisture 
which has called forth the filamentous character, for Fern-prothallia 
generally can only grow where moisture prevails. Four other species 
of Fern were found growing with the present prothallia, and all have 
prothallia of the type common in the Polypodiaceae. 
The prothallia of Schizaea bifida were found growing, some on 
damp sandy soil, others on clay soil. The ground was in places 
bare, but often partly covered with a growth of small Mosses and 
Hepaticae, and no doubt the filaments are sometimes an advantage 
to the prothallium in enabling it to rise up to the light between its 
1 Organographie der Pflanzen, p. 421. 
