253 
Pteridophytes . Are they vestigial? 
at the apex to a vegetative character. Abortive sporangia 
have been seen at the base of the strobilus in 5. spmosa , P. B. 1 , 
and in vS. Martensii , and would doubtless be found in many 
species 2 3 , but no isolated sporangia have been seen in the 
sterile region. 
The arrested sporangia at the base of the strobilus will 
bear the same interpretation as those in Lycopodium . Clearly 
the genus is in this, as in other respects, more specialized 
than Lycopodium . 
ISOETES. 
Wilson Smith 3 has pointed out in the case of /. echinospora 
that the sterile leaves differ from the sporophylls in their 
smaller size. But a closer study of the sterile leaves almost 
always ‘ reveals the presence of aborted sporangia.’ This 
observation led me to look over my old sections of Isoetes 
lacustris, with the result that sporangia in various degrees 
of abortion were found : in proportion as the spores are few 
in these, the sterile tissue is relatively bulky, but many of 
the sporangia remain quite small. Dissections showed that 
in the majority of leaves that are apparently sterile a rudi- 
mentary sporangium is really there, in the normal position. 
Wilson Smith remarks further (1. c., 324) that ‘the occur- 
rence of aborted sporangia on so many of the sterile leaves 
shows that all the leaves are potentially sporophylls, and 
suggests the probability that Isoetes has retained a more 
primitive form than any other vascular plant.’ This is clearly 
going too far 4 ; but none the less the fact that most of the 
leaves show abortive sporangia is interesting in relation to 
the question in hand. The irregular recurrence of the sterile 
and fertile zones is similar to that seen in the Selago group 
of Lycopodium . It would be important to know how early 
1 Gluck, Sporophyllmetamorphose, p. 355. 
2 See Studies, i, Phil. Trans., 1894, p. 522. I found them in all of the few 
species adequately examined. 
3 Bot. Gaz., 1900, vol. xxix, p. 323. 
4 Compare the remarks of Scott and Hill, Annals of Botany, vol. xiv, p. 443, &c. 
