352 Bower . — On the Structure of the Axis 
loculi would correspond to a unilocular one. I therefore put 
forward the hypothesis that such a sporangium as that of 
T mesipteris might be derived by partitioning from a sporangium 
such as that of Lepidostrobus , this hypothesis being in accord- 
ance with the observed details of development. Now the 
observations detailed above show that there is very close simi- 
larity between the vascular tissues of Lepidostrobus and those 
of the Psilotaceae ; and this evidence, coming as it does from 
a somewhat different quarter, appears to me to give material 
support to the hypothesis. On anatomical grounds the affinity 
of the Psilotaceae is clearly Lycopodinous ; all other Lycopods 
show uniformity in the general plan of the strobilus. These 
considerations should weigh with morphologists in favour of 
the theory that the synangium of the Psilotaceae is homo- 
logous with the sporangium of other Lycopods, that the 
sporangiophore is a branched leaf homologous with' the 
simple sporophyll of Lycopodium or Lepidostrobus , and that 
the single fruiting axis of Tmesipteris or Psilotum is comparable 
to a lax Lycopodinous strobilus. 
