REPRODUCTION 443 
into a special chamber inside the integument. Here it 
puts out tubes, but the tissue of the ovule breaks down, — 
drawing the pollen grain close to the necks of the arche- 
gonia. The cavity becomes filled with liquid, and the ciliated 
gametes, when discharged from the germinating pollen-grain, 
reach the female cells by swimming. The pollen chamber 
receives the pollen in all the Gymmnosperms, but in those 
with nonciliated gametes the pollen tube acts as the carrier 
of the gametes to the archegonia. 
In the Angiosperms one of the generative nuclei fuses 
with the oosphere. In many families the other one has been 
seen to fuse with the definitive nucleus. 
After the fertilisation of the oosphere in both cases an 
embryo is developed from it, which remains enclosed in the 
spore. In the Angiosperms fertilisation is followed not 
only by the formation of an embryo, but also by a large 
development of tissue arising in consequence of repeated 
divisions of the definitive nucleus, so that the spore con- 
tains a masgive so-called endosperm in addition to the 
embryo, the latter being usually embedded in the former. 
This so-called endosperm has thus a different morpho- 
logical value from the endosperm of the gymnospermous 
plant. 
One of the most remarkable features about the struc- 
ture and behaviour of the seed is the fact that soon after 
the embryo is formed it enters upon a period of rest, which 
in some cases is very prolonged. During this period the 
seed becomes detached from the parent plant. The re- 
sumption of its growth and development is known as the 
germination of the seed. This resting period does not 
occur during the development of the sporophyte in the 
Cryptogams. 
The embryo frequently attains a considerable size before 
its resting period commences. In this case it absorbs 
the contents of the cells of a considerable part, or some- 
times the whole, of the endosperm, so that it fills more or 
less completely the cavity of the spore. 
