245 
Cone and Fertile Stem of Equisetum . 
orders. Four unclosed meshes arise in the upper part of the cone. Above 
the last whorl of leaves the axis contains ten parenchymatous meshes. 
Three of the first order are closed in the neighbourhood of the insertion of 
the annulus on the axis. (The relatively wide third strand of the recon- 
struction arises by the fusion of two strands leading to the closure of a mesh 
below the level of the diagram.) Of the remaining seven meshes one is of 
the second order, being closed below the departure of the traces of the 
lowest whorl of sporangiophores ; six extend into the cone — one of the third 
one of the fourth, two of the fifth, one of the sixth, and one of the eighth 
orders. 
The widening of parenchymatous meshes commonly occurs by the 
dying out of tracheides above lateral or slightly internal traces, so that a mesh 
may become laterally biseriate in the second or later internodes through 
which it pursues its course. In Cone A of E. hyemale , however, the mesh 
lying above the eleventh and twelfth traces of the fifth whorl is laterally 
biseriate at its origin, i.e. the meshes above two sporangiophores are con- 
genitally fused. The mesh subtended by the bifascicular trace of the third 
sporangiophore of the sixth whorl of the same cone, though of much the 
same shape, is not truly laterally biseriate, as both bundles of this prema- 
turely divided trace enter a single sporangiophore (cf. Text-Fig. 2). 
There is one consideration in connexion with the closure of parenchy- 
matous meshes the significance of which was not as much emphasized as it 
should have been in my earlier papers on the cone of Equisetum , though 
the point was touched upon (Browne (1), pp. 680-1). It has already been 
pointed out that when the reduction in the amount of xylem at the nodes 
of the cone is greater than the reduction in the diameter of the stele, this 
leads to the formation of fewer meshes, but of meshes of a higher order 
(Browne ( 1 ), pp. 672-3, and ( 2 ), pp. 235 and 259). It is obvious that where 
a mesh is much narrowed at the height of a node and widens out again in 
the internode above, the formation of but little more axial xylem at the 
level of insertion of the sporangiophores would convert a mesh of a higher 
order into two of lower orders. For example, the presence of but a small 
amount of additional axial xylem between the sixth and seventh traces of 
the fourth whorl of Cone B of E . giganteum or between the seventh and 
eighth traces of the fifth whorl of Cone A of E. hyemale would, in the first 
case, convert a mesh of the fifth order into two meshes, the lower of the 
third and the upper of the second orders. In the second case it would 
substitute for a mesh of the third order two meshes, the lower of the first 
and the upper of the second orders. Similarly, the production of a little 
more axial xylem between the fifth and sixth traces of the second whorl of 
Cone A of E. arvense (Browne ( 1 ), p. 667), between the fourth and fifth 
traces of the fourth whorl of Cone A of E. palustre (Browne ( 1 ), p. 671), 
between the thirteenth and fourteenth traces of the second whorl of Cone B 
