445 
Phloem in the Stems of Dicotyledons . II. 
fate of these medullary bundles in the lower region of the stem was not 
ascertained. One or two internodes higher up they have increased in 
number by division and are thus smaller,, and for some distance upwards 
Fig. 20. Petasites officinalis. Petiole, showing well-developed medullary system of bundles. 
Bundles of adaxial portion of vascular ring at avr. x 4. Fig. 21. Rudbeckia laciniata. Vascular 
cylinder of stem, showing absence of medullary strands. x 4. Fig. 22. Rudbeckia maxima. 
Ditto, showing presence of medullary bundles (mb) ; la = lacuna, x 4. Fig. 23. Rudbeckia 
maxima. Leaf, showing complete absence of medullary bundles, x 4. Fig. 24. Echinacea 
( Rudbeckia ) purpurea. Vascular cylinder of stem, showing rudimentary central medullary bundles 
(mb), x 4. 
they traverse the nodes without any change in position or number. In the 
higher internodes they gradually dwindle in numbers as a result of fusion 
and of dying out in situ until, immediately below the second leafy node 
from the capitulum, they completely vanish; 
The lateral branches are quite devoid of medullary bundles. In the 
peduncle small vestigial bundles or phloem-strands occur on the ventral 
side of the bundle which leaves the vascular ring to supply a floret ; they 
arise de novo either in the sclerenchyma composing the ventral side of the 
bundle or free in the ground-tissue. 
