686 Browne . — Contributions to our Knowledge of the 
fuse and fill up the carinal canal (Ludwigs, pp. 401-2). Quite recently, 
Vidal has recorded all forms of thickening intermediate between reticulate 
and annular in the stem of E. pahistre (Vidal, p. 24). My observations, 
so far as they go, are in complete agreement with those of Queva on this 
point and in contradiction to those of Gwynne-Vaughan ; but they were not 
extensive, and were moreover limited to the fertile stem of three relatively 
small species in which the lateral metaxylem groups are not particularly 
well developed. 
In 1893 Cormack suggested that there were traces of secondary 
xylem in the nodal region of E . maximum (Cormack). Qudva, after 
a careful study of the ontogeny, pointed out that though the £ zone genera- 
trice ’ of the bundle persists later in the nodal region its activity is strictly 
limited, the divisions of its cells being merely the continuation of the earlier 
procambial division of the bundle ; thus its secondary nature is not proved 
(Qudva, pp. 33 and 36). Ludwigs is of the same opinion (Ludwigs, 
pp. 400-1). Nevertheless, Eames states that a few of the living species of 
Equisetum have been shown by Cormack to possess the remains of secondary 
xylem, and that Queva confirms the presence of such wood in E. maximum 
and records its occurrence in E. arvense . Eames further remarks that 
he has seen evidence for this ancestral character in both these species, 
in E. hyemale and in E. hyemale , var. robustum , A. A. Eaton. Finally, 
Ludwigs, speaking of the reticulate nodal tracheides, says : ‘ These vessels 
are supposed to be formed (“ sollen sich . . . bilden ”) from without inwards 
by the activity of a cambium and represent that which Eames would have us 
regard as centripetal wood 5 (Ludwigs, p. 400). It is hard to see how 
xylem-elements formed internally by a cambium could be anything but 
centrifugal ; nor does Eames regard the nodal xylem as centripetal. On 
the contrary, he expressly states that so far as he knows no question has 
arisen as to the centrifugal development of the nodal or supranodal wood, 
as he, in agreement with Jeffrey, calls it. He adds that it is clear that the 
innermost elements are protoxylem (Eames, p. 590). It seems clear that 
Ludwigs’ statement that Eames regards the nodal wood as centripetal 
is incorrect ; nor does Ludwigs himself express any agreement with this 
view. Whether the nodal wood is secondary or not is less clear ; on the 
whole its secondary character seems not to be proved ; though from the 
size of the Mesozoic Equisetales we should a priori regard secondary growth 
as an ancestral character, traces of which might well remain in certain 
species. 
At the level of the uppermost vegetative whorl of the fertile stem 
of E. limosum a diaphragm of the usual type was not found. At the node, 
owing to the junction of the xylem of the separate bundles into a con- 
tinuous ring, the separate endodermes of the internodal bundles are replaced 
by common inner and outer endodermes, this change being brought about 
