96 
Lady Isabel Browne. 
in Calamostachys is certainly a very strong argument in support of 
the non-phyllome view of the sporangiophore; but it has been 
shown that shifting of the position of the sporangiophores has 
certainly taken place in Palceostachya (5), another member of the 
Equisetales, and this shifting may also explain the arrangement of the 
parts in Calamostachys. The course of the vascular bundles supports 
this suggestion, for the vascular supply of the sporangiophore is, even 
in Calamostachys , where the sporangiophores stand mid-way between 
the whorls of bracts, given off from the cauline stele at the same 
point at which the bract-traces originate. But the principal reason 
for rejecting Professor Bower’s theory is that it does not give any 
adequate explanation of the structure of Sphenopliyllum fertile, in 
which the dorsal lobes (Professor Bower’s bracts) resemble the 
sporangiophores and hear sporangia of a perfectly normal type. 
Dr. Scott regards the fertility of the dorsal lobes as a secondary 
modification. This is perfectly legitimate for Dr. Scott, since he 
asserts the homologous origin of the sporophyte, but when it is 
acceded to by Professor Bower, one of the most convinced 
supporters of antithetic alternation, it appears to be much strained. 
It is surely illogical of Professor Bower, who has maintained at 
great length that the leafy sporophyte arose by progressive 
sterilization and elaboration of the zygote (1) (3), to suppose that 
pre-existing vegetative parts, such as bracts, suddenly became 
sporangiferous. He might of course regard this as a case of atavism, 
since the whole sporophyte is, according to him, sterilized spore- 
producing tissue ; this would indeed be a strained interpretation, for 
the bracts represent tissue that has, on his view, been sterilized for 
an immense period; in fact he regards these appendages as having 
been sterile ever since they arose. But even this possible, though 
fantastical, explanation does not account for the fact that this 
sporangium-bearing bract of his assumes all the characters of a 
sporangiophore. On the whole then it seems a fair conclusion that 
parts, such as the dorsal and ventral sporangiophores of Spheno- 
phyllum fertile, having a similar position relative to the axis, being 
apparently identical in structure and function, and bearing certain 
weil-defined identical organs (sporangia) are homologous. There 
are of course difficulties in applying Dr. Jeffrey’s and Dr. Scott’s 
theory (that the sporangiophores of typical Sphenophyllales are the 
ventral lobes of the sporophyll) to some members of the phylum ; 
such types as Sphenopliyllum majus and S. trichomatosum appear to 
have no sporangiophores. These may, on this theory, be accounted 
