5 88 
Eames . — On the Occurrence of 
Most Calamitean fossils consist of fragments of stems, or of casts of 
these, or of their internal cavities. Where the structure of tissues can be 
determined, the vascular system has naturally been best preserved. This 
system in the Calamites has been the subject of considerable investigation, 
and until recently its structure, in the stem, at least, was thought to be 
pretty well understood. But one of the older genera has lately been 
shown to possess a vascular structure previously unknown in this group, and 
of very great importance. The plant in question is from Lower Carboni- 
ferous strata, and has been named Calamites petty cur ensis by its discoverer, 
Dr. Scott . 1 
The suggestion that a new genus, Protocalamites , be founded upon it has 
been provisionally accepted by Dr. Scott, although he believes it may 
belong to the already established genus, Archaeocalamites . The vascular 
structure of the stem is like that of other Calamites, with one important 
exception — the primary wood developed both outwardly and inwardly 
from the protoxylem lacuna. We have in this plant the most ancient of 
the Equisetales showing distinct centripetal wood in the stem. 
In its anatomy Equisetum differs strikingly from the Calamites only 
in the lack of secondary wood. The secondary growth largely disappeared 
in the Equisetal stock at the end of the Permian period, although the 
Mesozoic Equisetales may have possessed it to some extent. A few even 
of the living species show remnants of such structure. In these cases, it 
occurs as a continuation in the growth of the most 4 woody ’ portion of the 
stem, the ‘nodal ring’, best called the supranodal wood. Cormack 2 has 
shown such development in Equisetum maximum , Lamarck ( E . Telmateia , 
Ehrh.), and Queva 3 confirms its presence there, noting it also in E. arvense , L. 
In E. hyemale , L. and its variety robustum , A. A. Eaton (E. robustum , A. Br.), 
as well as in the two above-mentioned species, the writer has seen evidences 
of this ancestral character. Often it appears most definitely in the rhizome. 
Doubtless other large and well-grown terrestrial species will show such 
conditions. In the much-reduced or semi-aquatic species, (E. scirpoides , 
Michx., E. fluviatile , L. (E. limosum , L.), and E. sylvaticum , L., no clear 
indications of cambial activity were seen. 
Since, then, our recent species possess so little secondary growth, 
comparison of their vascular system with that of their Paleozoic ancestors 
concerns chiefly the primary wood. Even here great reduction has occurred. 
In the internodes of Equisetum we find the fibro-vascular system to 
consist of a circle of separated bundles lying opposite the external ridges of 
the stem, just outside the large central cavity that occupies most of the pith. 
1 Scott, D. H. : On a Primitive Type of Structure in Calamites, Ann. Bot., vol. xv, p. 773 ; 1901. 
Studies in Fossil Botany, 2nd edition, p. 36, Fig. 11 ; 1908. 
2 Cormack, B. G. : On a Cambial Development in Equisetum. Ann. Bot., vol. vii, p. 63 ; 1893. 
3 Queva, C. : Histogenese et structure du stipe et de la fronde des Equisetum. Mem. de la 
Soc. d’Hist. Nat. d’Autun, t. xx, p. 21 ; 1907. 
