from 2 to 6 in most of the species, but in a few the num- 
ber may be 10 or even 12. There is considerable variation 
onasingle fertile segment. There is no indusium and the 
sorus is naked. Bower’ remarks that in the extreme cases 
of the gleicheniaceous sorus, with a large number of spo- 
rangia some of which are displaced by pressure, we find 
a condition which suggests the sori of both the Marat- 
tiaceae and the Cyatheaceae. In the former, the typical 
sorus is a single row of sporangia which surrounds a low 
receptacle. In the latter, the receptacle is elongated and 
its apex is covered with sporangia. In the eusporangiate 
Marattiaceae the spore-output is generally very large and 
in the higher ferns the spore-output is usually smaller. 
In the comprehensive genus G/leichenia it has been ob- 
served that the spore-output varies from 128 to 1024 and 
the number 256 is most frequent. Stromatopteris, on the 
basis of several spore counts, has a potential output of 
512. Platyzoma is particularly important in this connec- 
tion, because it exhibits a condition which is considered 
as incipient heterospory. ‘he sporangia are of two sizes, 
the smaller of which are more abundant. The number of 
spores varies from 16 downward in the larger sporangia, 
and from 32 downward in the smaller sporangia (Bower). 
There are intergrades between the extremes. 
This heterogeneous complex probably represents sev- 
eral relict lines of descent from a more extensive group, 
and the morphology of the spore-bearing members makes 
this suggestion more probable. 
It is advisable to append to this dicussion a few ad- 
ditional observations, though they are included only for 
the sake of completeness. 
Oligocarpia brongniarti Stur was believed by Zeiller” 
to have a uniseriate annulus, but recently De Pape and 
Carpentier” have figured a specimen which indicates that 
the annulus of the sporangium may be biseriate. 
[ 157 ] 
