68o 
Worsdell. — A Study of the Vascular System in 
The facts of the ontogenetic apical development of the stem would 
probably be of no use to us in settling this question, for the cortical bundles 
would probably be seen in process of formation above the insertion of the 
highest and youngest leaf, i. e. they ought to, from what we see in the 
mature structure ; the fact that these strands have no connexion with 
the central cylinder and only an indirect connexion with the leaf shows 
them to be caidine. 
During this sequence the dorsal midrib is early differentiated and 
remains unaffected by any subsequent events. 
The persistence of the inverted orientation of these bundles may 
perhaps be due to two physiological causes: (i) the fact that these bundles 
bear no relation to the stem-cylinder; (2) the fact that a dense arc of 
sclerenchyma occupies the dorsal (outer side), the usual position for the 
bast-fibres, causing the factor of orientation to become an indifferent one. 
Hence the structure of the leaf of Calycanthaceae is not so highly 
modified as would at first appear ; the presence of a dorsal arc of bundles 
only is merely apparent : the ventral system exists as well, but has become 
transferred, as in Paeonia , into the cortex of the stem . 1 
Thus we see that the structure of the Calycanthaceous stem is not 
so peculiar and so isolated as has hitherto been supposed ; in the preceding 
pages I have, it seems to me, fully accounted for its supposed vagary 
in possessing such peculiar structures as inverted cortical bundles. I have 
also accounted for and explained the meaning and origin, hitherto un- 
attempted, of the concentric cortical strands of Magnoliaceae and Paeonia . 2 
Throughout these various orders we find the different phylogenetic 
stages stereotyped in the actual structure of present-day species. This 
is especially well seen in the Anonaceae. In Artabotrys , Polyalthia , and 
Uvaria we see a primitive structure extending through the greater part of 
the leaf, the base only showing the more modified, advanced structure ; in 
Monodora , the structure which occurs only in the basal region of the leaf 
of Uvaria is here typical for the organ as a whole, indicating a greater 
advancement for the genus ; the arc-shaped contour of the lateral bundles 
in this plant ( Monodora ) represent in the ontogeny a congenital fixation of 
the lateral bundles of the leaf, but, on the contrary, they supply these bundles to the leaf ; they 
possess a cambium and a much larger amount of phloem than the lateral leaf-bundles ; their whole 
structure is different and more voluminous. Van Tieghem says that these bundles ‘ sont done, an 
meme titre que la stele, des Elements constitutifs de la tige, et e’est par erreur qu’on les a con- 
siders jusqu’ici comme de simples meristeles foliaires.’ I have arrived, quite independently of 
both these authors, at the same conclusion. 
1 This fact need not seem strange when we remember that stem and leaf are so intimately 
conjoined and related as I hold, on the phyton theory, to be the case. 
2 The structure of the peduncle in all three groups represents the ancestral point of common 
agreement and union, for this organ has varied less in structure in the course of evolution than has 
the vegetative stem ; hence the structure of the latter will represent the diverging lines of disagreement 
and separation ; but we must not be misled thereby. 
