Anatomy of the Cone and Fertile Stem of Equisetum. 677 
less commonly, between meshes that are closed before the apex of the cone 
is reached ; the two cases of confluence of meshes of Cone A are of this type, 
and another example may be seen above the insertion of the third whorl of 
Cone B. The reason why the confluence of unclosed meshes is commoner 
than that of closed meshes is that confluence means the dying out of 
a strand and thus reduces the number of members of the next whorl. Such 
reduction is, of course, especially characteristic of the upper part of the cone, 
and meshes arising above the upper whorls of sporangiophores have less 
Text-fig. 6. Longitudinal reconstruction of the xylem of Cone B ot E. limosum. Axial xylem 
black ; leaf-traces and parenchyma white. Magnification circa 16. 
chance of being closed, partly because they reach the apex of the cone 
if they persist through many internodes, and partly because they are 
continually widened by confluence with other meshes owing to the dying 
out of strands. Nor are these facts the only ones that indicate reduction of 
xylem ; the strands of xylem of E. limosum are much narrower, compared 
with the parenchymatous meshes separating them, than those of the other 
two species studied. 
The series of sections of Cone C of E. limosum was too short to afford 
reliable data as to the height of the meshes. 
