RAFFLESIA MANILLANA. 
223 
that the growth of the flowers of Rafflesia manillana interfers 
with the conducting power of the xylem of the host to only a 
very limited extent. This is due to the excessive development 
of the xylem which gives the parasite a firm anchorage without its 
penetrating deeply into the main tissues of the root. The great 
reduction in the vegetative parts of Rafflesia and the excessive 
growth of the tissues of the root around the shoot would seem 
to be a fine adjustment between host and parasite which is of 
great advantage to both. The developing flowers are furnished 
with an abundant food supply without destroying the tissues 
of the host to any considerable extent. It would seem, indeed, 
that the taking of food from the cells of the root is the chief 
damage which the parasite does to the host. 
SUMMARY. 
Rafflesia manillana is parasitic on the roots of a species of 
Cissus. The male and female flowers are similar in shape and 
color, and from 15 to 20 cm in diameter. The base of the flower 
is embedded in a vase-shaped mass of tissue formed from the 
root of the host. Pollination was not observed but is probably 
performed by insects. 
The ovules are small and exceedingly numerous. The embryo 
sac is of the usual 8-nucleate type. 
The vegetative portion of Rafflesia manillana consists for the 
most part of rows of cells but also of strands, plates and 
irregular masses of tissue. The rows of cells occur in the xylem, 
medullary rays, cambium, phloem and schlerenchyma of the host 
and apparently grow and multiply in all of these tissues, except 
perhaps the schlerenchyma. They seem to have little power of 
conduction and probably do but slight damage to the tissues of 
the host. 
The flowers originate from rows of cells which usually cross 
the cambium. The row of cells proliferates and forms a rounded 
mass of meristematic cells which becomes top-shaped by the rapid 
growth of the part in the bark. 
Layers of cork-like cells are frequently produced in the tissues 
of the host around the parasite. These may cut off the food 
supply of the latter and cause its death. 
The presence of the parasite causes an excessive growth of 
both the xylem and bark of the host in the region around the 
parasite and also a spreading apart of the xylem rays. This 
results in the formation of a vase-shaped mass of tissue in which 
