FORMATION OF CELLS. 
35 
present which have been formed by the division of the nucleus of the mother-cell. 
The next stage is that represented in //, where a lamella of cellulose, which has been 
formed in the cell-plate between the two nuclei, completely divides the mother-cell. 
Thickening takes place at the junction of this partition-wall with the wall of the 
mother-cell, and the protoplasm of the two daughter-cells becomes rounded off. In 
/rthe nucleus of each daughter-cell is seen to have divided into two; sometimes this 
division does not take place in one of the cells {V). A cell-wall is now formed simul- 
taneously between each pair of nuclei : a proper cell-wall is subsequently formed round 
each mass of protoplasm, the thick investing cell-walls undergo absorption, and the 
pollen-grains are set free.] 
I'he four cavities into which the mother-cell is divided in the development of spores 
and pollen-grains were at one time desig- 
nated the ' Special mother-cells ' of the 
pollen-grains, in which the grains them- 
selves were formed. The term is however 
inaccurate, because the four protoplasm- 
masses are themselves the essential parts 
of the new eel's, becoming subsequently 
enclosed in cell-walls. If the contents of 
the cavities are termed special- mother- 
cells, they are identical with the daughter- 
cells, i. e. the pollen-grains ; if, on the other 
hand, the term is applied to the walls of 
the cavities^ this is not in accordance with 
the present cell-theory. The term is in 
fact altogether superfluous. 
c. Cell-formation by Budding and Ab- 
striction. Among Fungi certain kinds of 
reproductive cells, conidia, stylospores, and 
basidiospores, are produced by small wart- 
like protuberances on a mother-cell, which 
then swell out and become rounded. The 
daughter-cell thus formed retains however 
at first its connection with the mother- 
cell at its base, the contents of the two 
being connected by a channel through this 
narrow portion. A septum is' eventually 
formed across this channel which splits 
into two lamellae, and in this manner the 
separation of the spore from its mother- 
cell is effected. The production of these spores therefore commences by a budding and 
is completed by division ; and the whole process may be termed Abstriction. It 
occurs in a typical form in the reproduction of the yeast-fungus {Saccharomyces). 
A wart- like out-growth from which several spores may be abstricted one after another 
is called a Sterigma ; when the mother-cell bears several sterigmata, as in the Basi- 
diomycetes, it is termed a Basidium. Intermediate processes between cell-formation 
by abstriction and ordinary cell-division occur when the protuberance is broad, and 
the daughter-cell therefore attached to the mother-cell by a broad base and separated 
from it by a broad septum, as in the branching of Cladophora ; or, on the other hand, 
when the terminal portion of a hypha is divided by septa, and the resulting cells 
become rounded off and detached, as in the formation of the spores of Cystopus, 
JEcidium, and other Fungi. [When the budding cell contains a single nucleus this 
probably divides, and one of the new nuclei goes to the bud ; when the cell contains 
several nuclei some of these travel into the bud.] 
Fig. 12. — / — VII Successive stages in the formation of the 
pollen of Ficnkia ovata (X S50). In VII the wall of the 
daughter-cell has absorbed water till it has burst ; its proto- 
plasm is forcing itself through the cleft, and is becoming 
rounded off. 
