RAFFLESIA MANILLANA. 
215 
multiply in the cambium, they grow only slowly, and do not mul- 
tiply in the wood and bast.” That the cells of Rafflesia manil- 
lana do not grow and multiply only in the cambium is shown by 
their presence in the primary tissues of the root. The greater 
development of the rows in the longitudinal and radial planes 
of the root than in the tangential or other planes may be due, in 
part, to their having been formed in embryonic tissue and then 
carried away from the meristematic region by the development 
of the tissues of the host, but it is also in the longitudinal and 
radial planes that the cells of the parasite could most easily push 
in between those of the host for it is in these planes that the latter 
are arranged in most regular rows. If the cells of the parasite 
did not grow and multiply in other than embryonic regions 
they would become separated by the growth of the host as in 
Brugmansia zippelii.^^ In Rafflesia manillana, however, the cells 
show little if any tendency to become broken by the growth of 
the host. In fairly large roots rows of cells several millimeters 
long may be found running radially in the wood. The appearance 
of the cells of the parasite would, moreover, frequently indicate 
that they were actively growing through the tissues of the woody 
cylinder and bark, and in the material examined they were cer- 
tainly relatively more numerous in the woody cylinder than in the 
cambium region. In other cases the arrangement of the cells of 
the parasite in the tissues of the host would seem to be due to 
their having pushed in between the cells of the root after the 
latter had ceased growing. 
The cells of Rafflesia manillana not only occur in the tissues 
of the host as rows of single cells but also, at times, as strands 
of tissue in the outer part of the bark of the root. Since these 
strands of tissue have not been seen in meristematic regions 
it would seem that they must have been developed in the outer 
part of the bark. Smaller strands (fig. 15), plates and irregular 
masses (fig. 16) of tissue are also frequently found in the woody 
cylinder. The strand of tissue shown in figure 15 is in the xylem 
of the root and can be distinguished from the latter by the con- 
tents and prominant nuclei in its cells. The plates of tissue 
usually lie in radial planes parallel to the longitudinal axis of the 
root. 
It would appear that the cells of Rafflesia manillana grow and 
multiply in all of the tissues of the host, but that growth is more 
active in the tissues of the woody cylinder than in the bark. In- 
dividual sections, however, show great variations in this respect. 
Peirce, Ann. Bot. 7 (1893) 291-327. 
