CELL-NUCLEUS—FERTILISATION 245 
developed within it a very rudimentary 
structure which it is possible to trace back 
to an extremely reduced prothallus. The 
pollen grain presently begins to put forth a 
tube which grows into the tissue of the stigma, 
feeding, like a fungal hypha, on the juices it 
contains. The tube grows down through the 
intervening tissue of the style into the cavity 
of the ovary. When it reaches this it is 
attracted to the tips of the ovules, and enters 
one of them by way of a little pore (the 
micropyle), burrowing through an intervening 
tissue of the sporangial (7. e. ovular) wall that 
may be present, until it reaches the spore. 
Meanwhile, from the body of the pollen 
grain the essential structures above alluded 
to have entered into the tube. Two sperms 
are developed, but they are not provided 
with locomotory cilia. They are finally dis- 
charged into the cavity of the spore, when 
they at once lose all cytoplasmic invest- 
ment, and appear as naked nuclei, somewhat 
vermiform in appearance. They pass through 
the protoplasm, which is contained in the 
spore (or embryo-sac as it is often called), 
apparently by autonomous movement, and 
one of them approaches, and finally fuses with, 
the egg. The other one fuses with a remark- 
able pair of nuclei which are found near the 
centre of the egg, and the nucleus resulting 
from the latter fusion is responsible for the 
production of the nutritive matter that 
later on fills so many seeds and grains (e. g. 
