certain Orders of the Ranales. 677 
proof, or at any rate, a large part of the proof, which is needed to show that 
the medullary or scattered system, along with that of the complete vascular 
cylinder, represents for both leaf and stem the primitive and original struc- 
ture from which all others have been derived. In the Calycanthaceae the 
dorsal arc of bundles in the petiole is normal and constant for the order, and 
hence this group may be said to be the most modified and recent of all as 
regards its actual petiolar vascular structure ; this, however, has not been 
followed by a corresponding advance in the floral structure, which remains 
one of the most primitive. Yet I shall presently show reason to believe, 
from a study of the real nature of the cortical bundles of the stem, that the 
real and essential petiolar structure is not so primitive as appears at first 
sight. 
As a result of this comparative study, we are also now able to explain 
the peculiar and characteristic cortical bundles of Magnoliaceae and Paeoni- 
aceae, as well as the famous inverted cortical strands of Calycanthaceae. 
The concentric bundles of the two former orders are seen to be merely 
Text-fig. 3. — Schematic representation of part of the petiolar vascular structure of Paeonia 
( A-C ) and Magnolia (Z>), showing phylogenetic origin of the concentric bundles from union of 
bundles belonging to the dorsal and ventral portions of the primitive cylinder of the leaf, vb — 
bundle of ventral part of cylinder. 
the expression of an imperfect transition from the complete cylinder to 
a simple dorsal arc of bundles , for all intermediate stages have been 
observed between the approach (in the base of the petiole or the cortex of 
the stem) of the inverted ventral bundles of the cylinder to those on the 
dorsal side and their imperfect union with the latter to form the concentric 
strand ; complete union, such as occurs in the majority of plants, consists 
not only of fusion but at the same time of a revolution through 180° on the 
part of the ventral bundle to form with the dorsal one a single collateral 
strand, one side only, of course, of each bundle being concerned in this pro- 
cess. In the cortical and petiolar bundles of Magnoliaceae and Paeonia 
and in the petiolar bundles of some Anonaceae and Berberidopsis fusion 
terminal position of the leaf, and which is gradually being lost, there would be no diminution in size 
or extinction of the bundles composing it as they gradually approach the base of the leaf. 
