592 REPRODUCTIVE ORGANS OF ALG. 
is furnished with two very long ciliz of excessive fineness. 
These antherozoids ultimately escape from the cell by a sudden 
movement resembling the action of a spring, and may then be 
seen to exhibit active movements in water. 
The nucule is regarded as a pistillidium, archegonium, or 
female organ. It is an oval sessile body, situated in the axil of 
a branch (fig. 856, s) ; it consists of a central cell with a double 
coat (jig. 860), surrounded by five cells, which are wound 
spirally round it, and terminating 
Fic. 859. Fie. 860. above in five or ten smaller cells the 
ends of which remain free ( fig. 859, 
a), and thus form a kind of crown 
at the apex of the nucule (jigs. 856 
A, ¢, and 859, a). Atanearly stage 
of growth the cells are separated 
from each other, and a canal is thus 
left between them extending from 
the crown towards the central cell. 
This canal is supposed to form a 
Fig. 859. Nacule or archegonium passage, by means of which the an- 
an ena Hig-atb. therozoids reach the central cell of 
Vertical section of a nucule. the nucule, by which its contained 
oosphere is fertilised. Ultimately 
the nucule drops off from its parent, remains at rest until the 
following season, and when it germinates first produces a single 
axial row of cells, forming a pro-embryo or pro-thallus from 
which the leaf-bearing sexual plant ultimately grows. 
4, Atca OR SEAWEEDS.—This order of plants, like the Fungi, 
comprises a very large number of species, which vary exceed- 
ingly in form, size, colour, and other peculiarities. They are 
all either inhabitants of 
water salt or fresh, or live 
on moist surfaces; and 
may be microscopic plants, 
or growths of enormous 
size. Adopting no special 
classification of the Alge, 
we willsimply describe the 
processes of reproduction 
occurring in certain ex- 
? amples as types of the 
Fig. 861. Filaments from a WVostoe colony. rest. 
After Luerssen. Nostoc, a very common 
Alga, is found living some- 
times in water, though more frequently on the damp surfaces 
of trees, stones, &c. It consists of a jelly-like substance, in 
which are imbedded moniliform threads of cells (fig. 861), the 
different filaments being interwoven with one another. The 
greater number of the constituent cells contain chlorophyll ; 
