The Principles of Morphology. 165 
Sphenophyllum Daivsoiti also homologous with a leaflet or segment 
of the sporophyll, for they are structures clearly similar in character 
to the sporangiophorcs of Tmcsipteris; and inasmuch as these organs 
in 5. Romeri connect those of S. Dawsoni and Cheirostrobus together, 
it follows that even the complex sporangiophore of this last-named 
plant is the homologue of a leaflet. And I maintain also that the 
case of Tmcsipteris shews that the synangium or compound 
sporangium, occurring in the best-known forms of Tmcsipteris , 
in Psilotum, and in 5. majus and S. trichomntosum, is also the 
homologue of a leaflet. And we may remind ourselves again that 
this ventrally-placed synangium or leaflet is merely the superior of 
the 2 or 3 original, terminal sporangia into which the still 
more primitive single terminal sporangium became divided. 
Passing on to the Calamarieae, let us imagine an axillary spor¬ 
angium like that of Sphenophyllum trichomatosum becoming elaborated 
into a peltate sporangiophore (it has been seen how just such an 
elaboration has taken place in the Sphenophyllales) ; we should 
then obtain the case of Palceostachya. But how are we to 
elucidate the relationship of the sporangiophores of Calamostachys? 
It seems highly probable that those of Cheirostrobus, Palceostachya 
and Calamostachys are each and all identical structures and that 
all must, therefore, be regarded as partaking of the nature of 
subdivisions of sporophylls, and not as independent organs. 
Bower well points out how the members of each succeeding whorl 
of sporangiophores are superposed to each other, and how the 
alternate succession of the sterile leaves is not disturbed by the 
intervening fertile whorls; also that the number of sporangiophores 
in a whorl is only about half that of the sterile leaves. These 
facts tend to prove that the sporangiophores are not independent 
foliar organs. Scott, finding a difficulty in regarding those of 
Calamostachys as of the nature of ventral lobes of the sporophyll, 
cuts the Gordian knot by the facile ascription to them of sui 
generis rank. This is also Bower’s view of the matter. 
Yet I cannot agree with Scott that the view which regards the 
sporangiophores of Calamostachys as homologous with those of 
Cheirostrobus is a forced one ; for it seems to me that there are clear 
grounds for holding such an idea and a relatively easy method of 
explaining the apparently independent position on the axis of the 
sporangiophores of Calamostachys. Holding the view, as I do, that 
each foliar organ possesses not only a “ foliar base,” confluent with 
the a>ffs below, but also a corresponding upward extension on the 
