97 
Sphenoft hy llales. 
for in three different ways. First, small and reduced sporangiophores 
may have been present and may be unrecognizable in the specimens 
known to us, which are merely impressions. Secondly the reduction’ 
foreshadowed in the last sentence, may have been carried so far 
that no traces of the sporangiophore remain. Thirdly it is possible 
that the so-called sporophyll of these types is in reality a lobe or 
sporangiophore of a sporophyll, and that these lobes, both of which 
must have been fertile as in S. fertile , have been separated from 
one another and now belong to successive whorls. This theory 
may appear strained, but in view of the fact that shifting of the 
sporangiophore has undoubtedly occurred in the allied phyllum of 
the Equisetales it affords a perfectly legitimate explanation. Miss 
Sykes has brought forward a theory somewhat similar to Professor 
Bower’s. She differs from him in regarding the sporangiophore 
not as an organ sui generis, but as a cauline structure or branch of 
the stem ; she agrees with him in regarding an axile position of the 
sporangiophore as primitive, and considers that it has, in the course 
of evolution, in many cases, been shifted until it became associated 
with a leaf or bract (11). This theory breaks down over the same 
difficulty as Professor Bower’s, for it affords no explanation of the 
case of Sphenophyllum fertile. If the sporangiophores are cauline, 
both “ ventral ” and “ dorsal lobes ” of Dr. Scott are, in Spheno¬ 
phyllum fertile, cauline, for they are fairly typical sporangiophores, 
and so far as we know, identical. But these dorsal sporangiophore 
of Sphenophyllum fertile are clearly the homologues of the dors a 
“ bracts ” of the typical species of Sphenophyllum and Cheirostrobus. 
These bracts are clearly phyllomes and not cauline structures; 
Miss Sykes herself admits this for Sphenophyllum Dawsoni, but 
their leaf-like character is even more marked in Cheirostrobus. The 
principal point in favour of Miss Sykes’ theory, though one not 
mentioned by her, is the fact that in Arclneocalamites, the oldest of 
the Equisetales, the sporangiophores are borne on the axis ; this, 
however, cannot weigh against so many other arguments. Miss 
Sykes : theory is grounded chiefly on an analogy with the Psilotacese, 
in which she regards the stalked synangium inserted on the upper 
surface of a lobed bract or leaf, as cauline ; but it will be shown later 
that the balance of evidence is against this view. 
But while agreeing with Dr. Scott’s view that the sporangio¬ 
phores represent lobes of the sporophyll, the present writer cannot 
adopt his conclusion that the fertility of the dorsal segments is a 
secondary modification. According to the theory of homologous 
