RAFFLESIA MANILLANA. 
213 
prophases. After becoming- considerably enlarg^ed the mega- 
spore mother cell divides into a small micropylar and a larger 
chalazal daughter cell. The micropylar daughter cell usually 
divides in a plane parallel with the longitudinal axis of the 
nucellus. The chalazal daughter cell divides unequally into two 
megaspores, the chalazal or innermost one of which gives rise to 
the embroyo-sac. The three micropylar megaspores degenerate. 
The embroy-sac is formed from the megaspore by three succes- 
sive divisions and is of the usual 8-nucleate type. It contains 
an egg, two synergids, three antipodals and two polar nuclei. At 
first it is somewhat elongated but as growth proceeds it becomes 
more nearly round. The antipodals are ephemeral and degen- 
erate early. The polar nuclei fuse without the occurrence of 
fertilization. No sign of fertilization has been observed in the 
material examined, and in old ovules the embryo-sacs had degen- 
erated. The rarity of Rafflesia manillana may well be due, in 
part, to the fact that its flowers are frequently not pollinated. 
In the cases observed the open flowers did not increase in size. 
The chief changes observed were that they turned black and 
shriveled to some extent while the tissues gradually died. The 
ovules remained about the same size. There was a tendency for 
the tissue around them to break down into a semi-fluid mass, 
in which they degenerated in a few days. The flowers became 
infested with a number of insects and larvae some of which bored 
from the outside into the cavity containing the ovules. This 
allowed other insects to enter the cavity, and several kinds were 
usually found within it. It is possible that the seeds, if formed, 
are disseminated by some of these insects, as the ovules are 
enclosed in the fleshy tissue of the flower and there is no evident 
means of seed dispersal. 
VEGETATIVE STRUCTURE. 
The vegetative structure of Rafflesia manillana is quite similar 
to that of the other species of the Rafflesiaceae, previously men- 
tioned. It consists, for the most part, of rows of single cells 
running through the bark, cambium, medullary rays and xylem 
elements. In the material examined these cell-rows occurred 
more frequently in the tissues of the woody cylinder than in those 
of the bark or in the cambium. In the woody cylinder they were 
about equally frequent in the medullary rays and xylem elements. 
They were, perhaps, somewhat more numerous in the phloem and 
sclerenchyma than in the parenchyma of the bark. The cells 
composing the rows are usually fairly short, rather densely filled 
with protoplasm, and each contains one prominant opaque nu- 
