
No. 461.] AFFINITIES OF EQUISETUM. 281 
“astelic’ type, to which Ophioglossum also belongs. Whether 
or not Equisetum is astelic in Van Tieghem’s sense, there is a 
very important respect in which it differs from the other pterido- 
phytes that have been critically studied, namely, the origin of 
the vascular bundles from the cortical region, and not from the 
primary central cylinder. A longitudinal section of the shoot 
shows an early differentiation into a central cylinder and cortex, 
but it is from the latter and not from the former that the vascu- 
lar strands originate, the central cylinder developing only the 
pith. 
Jeffrey in his study of the development of the vascular sys- 
tem in the young sporophyte does not state whether the rela- 
tion of the vascular strands to the primary central cylinder is 
the same as in the adult sporophyte, but there is no reason why 
it should be different, as otherwise the arrangement of the bun- 
dles is the same. 
He states that the arrangement of the bundles in the primary 
shoot is the same as in the later ones, except that he finds at 
the base of the shoot below the first leaf sheath, a closed ring 
of vascular tissues, such as occurs at the nodes, and considers 
this as a remnant of a primitive cylindrical stele or vascular 
cylinder; but it is not quite clear why this does not simply 
represent the first node where we should expect to find essen- 
tially the same arrangement of the tissues as in the later nodes. 
As in the later shoots, there extend between the nodes sep- 
arate vascular strands corresponding in number to the teeth of 
the leaf sheaths, — three as a rule in the primary shoot. These 
fork at the nodes, and each branch joins one from the neighbor- 
ing bundle, so that the vascular strands alternate in succeeding 
internodes as they do in the later formed shoots. 
In Archzocalamites, the earliest known type, the bundles are 
continuous from one internode to another, but in the Calamites 
of the Carboniferous, the same arrangement is found as in 
Equisetum. 
Jeffrey considers the spaces between the internodal strands 
as gaps in an originally continuous cylinder, comparable to the 
cylindrical stele of the ferns, or 
large foliar found in the 
: pom branches are given off, in the - 
the ramular gaps, occurring where 
