RAFFLESIA MANILLANA. 219 
tendency for the cells between the bundles to divide and produce 
a cambium. This process, if continued, would produce a con- 
tinuous ring of cambium. Soon, however, the cambium instead 
of forming such a ring grows around each bundle, the result 
being that each bundle comes to have a concentric arrangement 
(fig. 24), as in Brugmansia zippelii ^^ and Rafflesia rochussenii^^ 
While the vascular bundles and cambium are making their 
appearance, an apical growing region is also in the process of 
differentiation. This latter is preceded by the formation of a 
cap over the apex (fig. 20). Since the whole surface of the 
parasite is joined to the host it would seem that the apex of the 
shoot could not become a growing region, which would cut off 
the bracts and floral parts, unless there were some process 
whereby the growing region would be separated from the host. 
Apparently the function of the cap is to cause this separation. 
The cap is formed from a layer, several cells thick, which ex- 
tends over the upper surface of the parasite (fig. 20). Growth 
apparently ceases in these cells, after which they become 
stretched by the enlargement of the part of the parasite below 
them. A split then comes in between the cap and the under- 
lying tissue, while the cap remains firmly attached to the bark 
of the host. The apex of the shoot, beneath the cap, is then 
organized into a growing region from which the bracts and 
floral parts are cut off successively (figs. 21, 22, 12, 13). The 
cap continues to be attached to the bark of the host for a con- 
siderable period. In figure 21 this shows as a dark streak just 
under the bark of the host. A large part of the short stalk of 
Rafflesia manillana is formed from the apical growing region 
and the parasite again becomes top-shaped (figs. 21, 22). The 
rapid enlargement of the bracts and floral parts causes the 
cells of the shoot to be arranged in rows more or less perpen- 
dicular to the axis of the shoot (figs. 21, 22). 
The average bundles of Rafflesia manillana, which show as 
dark streaks in figures 19 and 22, connect with the host in the 
general region of the cambium. The exact point of connection 
varies in the same and different specimens. What is perhaps 
the most usual arrangement is for the cambium around the outer 
part of the bundles of the parasite to end in approximately the 
region of the cambium of the host. In other cases, however, 
various parts of the cambium of the parasite may be in con- 
nection with that of the host or the cambium of the parasite 
"Peirce, C. J., Ann. BoU 7 (1893) 291-327. 
"Schaar, F., Sitzher. Acad. Wien 107 (1898) Abt. 1: 1039-1056. 
