440 Browne . — A Fourth Contribution to our Knowledge of 
never become free from those of the axial bundle, and a few sections higher 
up the latter has resumed its normal appearance. 
Above the last whorl of leaves the cone-bearing branch of E. debile is at 
first smooth and unribbed. In the two axes bearing the mature cones 
A and C the grooving soon reappears, the ribs being in fact particularly 
prominent. But, unlike the other ribbed axes of Equisetum , the ribs are 
opposite the vallecular canals, and the grooves opposite the bundles (cf. 
PI. XXI, Fig. 6). 1 
Though Milde records (p. 135) the occurrence of stomata on the dorsal 
and more rarely on the ventral side of the leaf-sheaths he does not mention 
their presence on the annulus. In Cone B of E. debile , however, the upper 
surface of the annulus bore several stomata (PI. XXI, Fig. 9). Though this 
species belongs to Milde’s Equiseta cryptopora , characterized by a very 
regular arrangement of the stomata, those of the annulus appear to be 
few and irregularly distributed. 
In Cones A, B, C, D, and E of E. debile the region transitional from 
branch to cone shows a rather wide range of variation. In Cones A and D 
there are, in the internode below the annulus, respectively nine and five vascu- 
lar strands. These have arisen in the manner usual in the genus, i. e. by the 
breaking up of the ring of nodal or supranodal xylem into bundles equal in 
number to and alternating with the uppermost leaf-traces. But in Cone B 
there were only five strands throughout the greater part of the internode 
below the annulus, although the last whorl of leaves and the first whorl 
of sporangiophores both consisted of eight members. A sixth strand was, 
indeed, constituted, but it died out almost at once. Over two of the leaf- 
traces no fresh parenchymatous mesh arose, but owing to the rapid widening 
of the five existing meshes as they pass upwards, all the strands soon 
become narrow bundles, much of the same size. In Cone C of E. debile , 
where the last foliar whorl consisted of six, and the basal whorl of the cone 
of seven members, there were only five strands in the internode below the 
annulus. This is due to the fact that at the last node of the branch the ring 
of reticulate tracheides was not complete. A parenchymatous mesh, though 
markedly narrowed at the node, persisted through the latter. Consequently 
the traces on each side of the mesh were very near the edges of the band of 
xylem ; above their departure the mesh between them widened again, but no 
fresh meshes were formed. A like failure to form a complete ring of wood 
at the last node of the branch bearing Cone E and a similar structure above 
the traces next to the persistent mesh account for the reduction of the 
vascular strands to four in the infra-annular internode of Cone E, in which 
1 Duval-Jouve . (p. 190 and PI. V, Fig. 13) states that in the obscurely ribbed rhizome of 
E. littorale the carinal canals lie opposite the grooves and the vallecular canals opposite the ribs. 
According to his description the large size of the vallecular canals appears to cause the tissues 
external to them to be pushed outwards, so as to simulate a blunt rib. Milde, however, after 
examining numerous specimens, was unable to confirm this observation (Milde, pp. 360-1). 
