206 WorsdelL — The Vascular Structure of 
of this part is often prolonged into a short acuminate blade, 
recalling its foliar nature, or it may be produced on each side 
into two reflexed horns. 
The numerous bundles which are found in the stalk of this 
organ usually have their origin in a single bundle which is 
given off as a lateral branch from one of the members of the 
central cylinder of the axis of the cone ; this bundle, while 
traversing the cortex, divides into two, and these in the base 
of the sporophyll split up at first into three and very soon after 
into a larger number. Occasionally the two bundles may 
arise separately and independently from the cylinder of the 
axis. The bundles of the stalk are usually of small size, 
their xylem being mainly of centrifugal origin, sharply defined 
and deeply staining with safranin, and often, but not always, 
accompanied by a (usually) much smaller quantity of centri- 
petal xylem, which, however, is not so sharply defined nor so 
brightly stained, the tracheides of the centrifugal portion being 
evidently better lignified and chiefly functional in conduction. 
In proportion as the bundles pass up into the flattened portion 
of the sporophyll bearing the sporangia, the centripetal 
increases and the centrifugal xylem decreases in significance 
and quantity, until, in the sterile portion above, the former 
predominates. In this latter portion the structure of the 
bundles is essentially the same as that in the foliage-leaf. 
The centripetal xylem is as sharply defined as, and often even 
of a brighter colour, than the centrifugal, and is usually 
present in greater quantity. The bundles are of very varying 
sizes ; they have no definite orientation, lying in all directions. 
They arise from successive branching of those in the stalk. 
They have no longer any important conducting function to 
perform, the xylem being probably chiefly serviceable as a 
strengthening framework, so that the phloem is usually 
reduced in quantity and definiteness. The change of function 
of the bundles in this region and their relative unimportance 
will probably have much to do with the inconstancy of 
structure displayed, for the two kinds of xylem are very 
unequally developed in different bundles, the one often 
