Strobilus in Archegoniate Plants . 353 
with the facts of formation of septa above noted, will be, that there 
is no fundamental difference between sterile tissue of a septum and 
sporogenous tissue , since both appear to be mutually convertible. 
Lastly, I would point out that the arrest or sterilization 
may involve a whole sporangium. If the strobili of species 
of Lycopodium or Selaginella be examined, it will be found 
that, passing downwards from the base of the strobilus, 
sporangia are to be seen in the normal position, but succes- 
sively of smaller size, till a small sterile group of cells is all 
that represents the sporangium : finally the sporangium dis- 
appears altogether. A similar state of things is found at the 
apex. Again, in such species as L. Selago there are suc- 
cessive sterile and fertile zones, which graduate off into one 
another through zones showing such successive series of 
abortive sporangia as those above noted. Similar imperfect 
bodies (synangia) are frequently found at the limits of the 
fertile zones in the Psilotaceae, while the fertile spike of 
Ophioglosstim may also be represented by a small non-fertile 
body. How are these facts to be regarded from an evolutionary 
point of view? Are the small non-fertile bodies nascent 
germs of sporangia, or are they vestigial ? As a third alter- 
native it may be suggested that they have no phylogenetic 
bearing whatever ; but considering the frequency of their 
occurrence, and the gradual steps of their arrest, I do not 
think this last view to be a probable one. I think we 
can only consider them to be vestigial organs : potential 
sporangia, arrested, and in the down-grade of development. 
Their occurrence is doubtless very closely connected with the 
physiological position of the plant which bears them, but the 
recognition of this does not in any way explain away the 
interest which attaches to their frequent presence. The leaves 
which subtend the sporangia (sporophylls) differ in many 
species of Lycopodium from those which do not (vegetative 
leaves), though their relation to the axis is the same : in 
passing from the strobilus to the vegetative region a gradual 
transition from sporophylls to the vegetative leaves is seen, 
and it proceeds parallel with the arrest and final disappear- 
