214 W or s dell . — The Vascular Structure of 
evidently of primary origin, but a small segment of the 
cylinder is probably formed of purely secondary tissue, 
though this is not perfectly certain ; but no crushed phloem- 
elements are observed at the periphery of this part. In the 
central parenchymatous tissue, or pith, of the strand occur 
a few tracheides isolated or in groups, some of which are 
attached to the protoxylem ; they do not extend to the 
centre, but quite a small central free space is left ; they 
evidently belong to the primary centripetal system (Fig. 4). 
This concentric strand, for about three-fourths of its con- 
tour, has small inverted strands attached to it, whose tissues 
appear to be mostly secondary ; there is no sign of primary 
phloem anywhere, no crushed elements of the latter being 
visible, most of the elements in this region occurring in the 
same radial rows with cambial cells. But the xylem of these 
strands, besides the numerous layers of secondary tracheides, 
has in all cases some primary xylem, some of the elements 
being small, others large and developed as transfusion-tissue 
with reticulate thickenings on the transverse wall, which 
occur both in a lateral and a ventral position, often in great 
quantity. In only one of these small bundles could I 
discern any sign of protoxylem, in most this tissue appears 
to be absent. In one or two cases there seems to be a con- 
siderable quantity of primary centrifugal xylem. In the 
tissue below the place of insertion of other megasporangia 
the strands are quite collateral, with a few centripetal 
tracheides, of which, in one instance, a radial row of three 
was attached to the protoxylem ; a sheath of stone-cells 
extends round close to this row of tracheides. In some of 
the bundles a large amount of transfusion-tissue runs out 
amongst the cells with conspicuous nuclei and dense pro- 
toplasmic contents occupying the region between the strands 
and the sheath. 
In the sterile region of the sporophyll, above the insertion 
of the sporangia, the bundles are much reduced as regards 
their centrifugal xylem and their phloem, so that the former 
approximates more to the dimensions of the centripetal xylem, 
