440 
WorsdelL — Origin and Meaning of Medullary 
are seen to have an arc of three or four small normally-oriented bundles around 
their xylem. Such curious groups of concentrically-arranged bundles are 
what one so frequently encounters in the leaves of this order ; it is 
exceedingly rare to find such bundle-groups passing in® as in this case, 
to constitute part of the stem-ring ; it must be regarded as one of the 
primitive features of this last. 
The great radial thickness of the ring, consisting of scattered bundles, 
the very diverse orientation of the latter, their great variation in size, the 
presence of numerous rudimentary bundles intercalated amongst the others, 
must all be regarded as primitive features, for none of them can be solely 
explained on the grounds of adaptation to the very large capitulum with its 
great multitude of florets. For there is clearly no reason why the bundles 
should be scattered instead of being ranged in line, nor why they should 
be diversely orientated, or of different sizes and degrees of development. 
It is simply that the considerable thickness of stem in this plant affords 
room and play for the original primitive structure of the cylinder ; hence 
this has been retained. 
C. Scolymus, L. 
Peduncle. 
All the features described above for the stem of that species are present, 
especially in the upper part of the peduncle of this species, in a greatly 
accentuated form. The structure probably represents the m6st extreme 
Fig. 15. Cynara Scolymus. Segment of vascular cylinder and cortex (V) of uppermost portion 
of peduncle, showing the scattered disposition of the bundles. Some of these are inversely orientated 
(ib ) ; others are partially amphivasal ( ab ) ; others lie sideways. There is here no distinction 
between medullary strands and those of the ring. x 4. Fig. 16. Cynara Cardunculus. 
Petiole, showing scattered disposition of the bundles, x 4. 
case in the Compositae of the primitive scattered disposition of the bundles 
composing the vascular ring (Fig. 15). The radial thickness of the ring 
here equals the diameter of the pith. The majority of the bundles are 
much smaller than those of the stem of the last species, and there are 
a larger number of rudimentary strands. A few of the innermost bundles 
are completely amphivasal, which is another primitive feature to be added 
