Phloem in the Stems of Dicotyledons . II. 441 
to those already enumerated. Most of these bundles represent traces from 
the large involucral bracts. There is no discernible limit between stele 
and cortex. 
Leaf. 
That the extremely marked scattered disposition of the bundles in the 
stem and peduncle has no direct connexion, as regards origin, with the 
supply of the numerous florets in the capitulum is shown by the fact that 
this same scattered arrangement occurs in pronounced form in the petiole of 
the leaf (Fig. 16). The bundles are less numerous relatively to the available 
space, but exhibit the same differences in size and orientation, and are also 
here and there in a rudimentary condition. None of these features can be 
represented as in any sense adaptive to the needs of the plant ; it therefore 
follows that they are primitive and ancestral. This conclusion thus applies 
to the structure of both leaf and stem. According to the view which is 
set forth throughout this paper, the leaf has imposed its structure on the 
stem, not vice versa. 
Centaurea. 
Stem. 
In C. macrocephala , Puschk., there is a very large capitulum ; this 
implies a stout roomy stem and peduncle to support and feed it. Hence 
this allows space for the primitive scattered disposition of the bundles to 
reappear, which is, in fact, what we find in this species. All the features, 
with the exception of amphivasal bundles, described above for Cynara 
occur here, but on a very reduced scale. 
In all other species the bundles are almost in line, though the ring 
betrays in every case its derivation from a scattered system of bundles. 
Arctotideae. 
Gundelia Tournefortii, L. 
Stem. 
Herbarium material only was investigated. 
Small phloem-strands occur scattered, at wide distances apart, in the 
pith (Fig. 17). 
Senecionidae. 
Senecio Petasites, DC. 
Stem . 
At the periphery of the pith and opposite, and exactly median to, 
the arc of leaf-bundles in the cortex which has recently left the vascular ring, 
occur five or six rudimentary medullary strands, one or two being attached 
