Anatomy of the Cone and Fertile Stem of Equisetum . 687 
in the manner already described by Pfitzer (Pfitzer, pp. 33^~7)‘ The 
same author has noted that in the nodal region the cells of the outer 
endodermis have for a little distance thicker walls (1. c., p. 33 2 )* ^ have 
observed the same phenomenon in E. limosum . A little above the depar- 
ture of the leaf-traces, where the ring of nodal xylem breaks up, the endo- 
dermis consists of relatively thick-walled cells that stain very deeply with 
Bismarck brown ; as the breaking up of the ring proceeds these dark brown 
cells become involuted round the bundles through the parenchymatous 
Text-fig. 8. Reconstruction of uppermost part of fertile stem of E. limosum. n.x. — nodal 
wood, breaking up into the bundles ( b ) of the internode above ; l.t. = leaf-trace ; i.b. = bundle in the 
internode below; p. = parenchyma between the bundles; p} = torn parenchyma on the inner side 
of the bundles ; end. — endodermis ; sc.co. — inverted hollow cone of sclerenchyma. 
meshes of the upper internode ; thus we get a ring, three to four cells deep, 
of these dark brown cells lying inside the circle of strands ; traced upwards 
this ring communicates through the parenchymatous meshes with the dark 
brown cells of the outer endodermis. Traced downwards into the lower 
internode the ring of thickened cells narrows rather rapidly ; at first it 
is connected with the narrow band of parenchyma that persist on the inner 
side of the vascular bundles ; but as we pass downwards it narrows so 
rapidly that in the mature stem is soon ceases to be in contact with this 
parenchyma, and in a transverse section lies free in the middle of the central 
cavity (Text-figs. 8 and 10 ). The thin-walled elements internal to this ring 
