690 Browne. — Contributions to our Knowledge of the 
and the endodermal cells lying on the inside of the bundles are thickened, 
and the thickenings are dark brown. This thickening and colouring of the 
layers of thickening spreads a little higher up to the pith cells, so that we 
get a polygon of which the blunt ends project between the special endo- 
dermes. Thin-walled cells are often found inside this polygon (Pfitzer). 
Jeffrey, working on E.hiemale , also records sclerized brown cells. He 
writes of his Fig. 2 , PL XXIX, representing a tangential section of the nodal 
region of E. hiemale : 6 The magnification is sufficient to show that the 
medulla of the branch is composed of brown sclerenchymatous cells * 
(Jeffrey, 1). As the photograph is of an obliquely oriented organ it is not 
easy to make out the exact form of the sclerenchymatous mass ; from the 
above quotation it might be thought that the whole medulla is sclerized, 
but it is hardly safe to conclude this from a passing reference like that 
quoted above. Jeffrey states, too, that the diaphragm of the first node of 
the branch is very deep, and somewhat sclerified at the ends ; this diaphragm 
does not appear to be connected at the origin of the branch with the above- 
mentioned mass of sclerenchyma. He also found that in the main stem of 
E. hiemale and E. limosum the diaphragm was partially sclerified ; this he 
regarded as sclerified periderm and compared it to the non-sclerified 
periderm in the diaphragm of certain Catamites. 1 
The Transition from Fertile Stem to Cone. 
The annulus seems to mark the position of a reduced node, and the 
reasons for this must be examined. We have seen from the anatomy of the 
cone and stem that fresh parenchymatous meshes arise above the nodes ; 
usually they arise at a relatively small distance above a trace that has 
departed ; we have also seen that the closure of meshes of the internode 
below is effected in the region of the node. This closure of parenchyma- 
tous meshes and the formation of fresh ones in the region of the node causes 
a branching of the vascular strands at this level. We have seen also that 
when the xylem is much reduced at a node certain of the strands pursue an 
isolated course upwards into the next internode because sufficient xylem to 
close the meshes of the internode below is not present, and because the 
trace-bearing strand remains too narrow to give rise to an independent 
parenchymatous mesh above the node. We may generalize as to the 
fluctuating conditions obtaining in the fertile nodes by saying the greater 
the reduction of nodal xylem the larger the proportion of strands that pass 
through a node without branching. In the vegetative axis in which the 
nodal xylem is well developed and forms a complete ring (though the 
internodal xylem is less developed than in the cone), all the meshes are 
1 Since writing the above 1 have come across H. H. Thomas’s record of a nodal diaphragm, 
hollow in the middle, in a Jurassic species of Equisetites. Cf. Memoires du Comite Geologique de 
Saint-Petersbourg, N. S. 71, 1911. 
