2i8 W or s dell . — The Vascular Structure of 
and the nervation to which it gives rise, though imperfect, are 
not nearly so rudimentary and reduced in character as the 
one above described, for the bundles composing it are 
perfectly functional and nearly everywhere continuous ; the 
tip of the organ is occupied by 3-5 bundles formed by 
the division of one of the two main branches of the bundle 
coming from the axis ; these bundles have the structure 
characteristic of those in the sterile portion of the sporophyll, 
while the large bundle in the lower part has an endarch 
structure. The presence of these bundles in the cortex 
supplying the barren sporophylls was observed in two or 
three female and also in several male peduncles ; they were 
most abundant in the former, where they often occur in 
longer* or shorter and very straight tangential rows in the 
outer part of the cortex, but may also occur quite isolated. 
Most of these bundles possess, besides the usual endarch 
portion, two, often very large, groups of centripetal xylem, 
lying each slightly to one side of the median ventral line, and 
with tracheides of which those farthest towards the ventral 
side are three or four times the size of those composing the 
centrifugal xylem. Protoxylem is seen to be attached to 
each group (Fig. 9). But there is considerable variation in 
the development of these centripetal xylem groups, for they 
may be very much more reduced than those shown in Fig. 9, 
or even almost entirely absent ; they may be also in much 
closer connexion with the centrifugal xylem, or even, as in 
the case of one such group belonging to a bundle in a male 
peduncle, perfectly continuous therewith. 
The reason why I attach special importance to these 
bundles arises from the fact that I regard each such bundle, 
with its three distinct groups of xylem, as the vestige of 
a primitive concentric leaf-trace bundle which was probably 
characteristic of the ancestors of these plants. Now in the 
cortex of the stem of certain species of Medullosa just such 
concentric leaf-traces are known to occur, which during their 
course outward become split up into three portions, the 
concentric structure becoming thereby lost. My Figure 9 
