SUMMARY 427 
primitive position till maturity. But in the Equisetales the pendulous 
position is gradually assumed, the inversion of the sporangia being 
brought about by active growth of the middle region of the sporangio- 
phore. This inverted position was probably a derivative state, as indeed 
its gradual appearance in the development of the individual would seem 
to indicate. The result presumably of a similar inversion is seen in 
Cheivostrobus and in S. Rémeri, while it appears to have been general 
in the Equisetales. 
This discussion leads naturally to the question whether in the cases 
before us the synangial state, as seen in the Psilotaceae and in S. majus, 
is the more primitive, or that with separate sporangia, as seen in Egudsetum 
or in Cheirostrobus. So far as individual development can serve as a 
guide it would point to the former, for in their first stages all sporangio- 
phores are synangial, and the state as seen in the Psilotaceae is merely 
the consequence of maintaining to maturity the relation of the loculi as 
at first initiated. The condition seen in Agudésefum, on the other hand, 
is a consequence of the individual projection of each developing sporangium. 
When this is considered together with the inversion which goes along with 
it, it would appear probable from the story of development that the erect 
synangial condition was relatively primitive, and the condition with separate 
inverted sporangia a derivative state. 
In view of the initial synangial condition of all young sporangiophores, 
the further question arises of the origin of the whole structure in descent. 
It has been designated a placental growth: is there any clue from develop- 
ment how it came to be? It has been pointed out (p. 414) that in the 
young sporangiophore of Zmesipter’s the origin of the tissue of the sterile 
septum which separates the sporangia is similar to that of the sporogenous 
tissue, while in certain reduced sporangiophores the septum may itself be 
sporogenous. These facts point, in the simple case of Zmeszpteris, to the 
conclusion that the septum is not essentially different from fertile tissue, 
and suggest that the whole body arose from the subdivision of a single 
sac, together with upgrowth of the adjoining tissues. In fact, that the 
sporangiophore is really a form of sorus, resulting from septation of a 
primitive fertile loculus, together with upgrowth of its receptacle or 
placenta: the separate loculi would thus be carried outwards with its 
growth. The facts of development as well as of distribution of the sporan- 
giophores readily coincide with this view of its probable origin. There 
is a biological probability that this mode of progression to a more complex 
state should occur, for the nourishment of separate loculi is more readily 
carried out than that of one large one, while the scattering of the ripe 
spores is more certain where the sporangia project. Lastly, there is 
precedent for the conversion of sporogenous tissue into sterile in Jsoefes, 
and apparently also in Lepidodendron, while numerous Angiosperms show 
septa in the anther, formed by sterilisation of fertile tissue in the manner 
here suggested. 
