696 Browne . — Contributions to our Knowledge of the 
be of the same nature may be seen in one of Kidston’s figures of Pothocites 
(Kidston, PL XII, Fig. 14). 
General Considerations. 
Equisctum is so isolated among existing plants that comparisons of 
the structure of its cone with the cones of recent plants seem at present to 
be futile from a morphological point of view. But the phylum of the 
Equisetales was well developed in the past, and a comparison with the 
varied cones of this great phylum offers the most promising field for con- 
clusions as to the comparative morphology of the cone. The cones of the 
Equisetales may be divided into two great groups, those consisting only 
of fertile appendages, provisionally called sporangiophores, and those in 
which the cone also contains sterile appendages. Leaving abnormalities 
out of consideration the former group includes the cones of the recent 
Equisetum y those of the species of Equisetites in which the reproductive 
organs are known, namely, the carboniferous E. Hemingwayi , Kidston, 
the Liassic E. Nathorsti, Halle, and the Rhaetic E. suecicmn , Nathorst 
(Halle, pp. 27-31); it also includes the cones of Autophyllites furcatus , 
Grand’Eury, Bornia p achy st achy a, Bureau, and perhaps of B. transitions, 
Grand’Eury ; these three species come from the Carboniferous (Jongmanns, 
pp. 265-7). In the cones forming the so-called genera Calamostachys 
(including Renault’s Calamodendrostachys Zeilleri ), Palaeostachya , Hut - 
tonia , Cingularia , and in Volk man n ia psendosessil is, Grand’Eury, sporangio- 
phores and sterile bracts succeed one another on the axis of the cone 
(Jongmanns, p. 279). These types of cones are of Palaeozoic age; most 
of them certainly, probably all of them, represent cones of the Calamariae 
in the widest sense of the word. In Calamostachys bracts and sporangio- 
phores form equidistant whorls ; in Palaeostachya the sporangiophores are 
inserted in the axils above the bracts, while in Huttonia , in Cingularia , and 
in Volkmannia pseudosessilis they are situated below the bracts. Archaeo- 
calamites (including Pothocites and Bornia , excepting perhaps B. pachysta- 
chya and B. transitions ) appears to be intermediate between the two groups, 
for its cone consists of whorls of sporangiophores, sometimes at least inter- 
rupted at considerable intervals by a whorl of sterile bracts. The best way 
of elucidating the anatomy of a cone is certainly by the study of its internal 
structure. But nearly all the cones mentioned above are known as im- 
pressions only; we are, however, acquainted with the anatomy of some species 
of Calamostachys and Palaeostachya . It has been customary of late years 
to regard the sporangiophores and bracts of these two genera as phylo- 
genetically lobes of a compound leaf of sporophyll. Such a view is admit- 
tedly based partly on an analogy with the Sphenophyllales, in which group 
the sporangiophore, when present, is usually inserted on a sterile bract. This 
view has been somewhat widely held, and different modifications of it were 
