THALLOPHYTES. 
the enveloping tubes does not begin till a later period; the coils become gradually 
flatter while the apical cell of the branch increases considerably in size and developes 
into the oosphere (Fig. 199). The development and fertilisation of the carpogonium 
of Chara has recently been described in detail by De Bary in the case of C. foetida. 
Here also it consists, from an early stage of its development, of an axial row of three 
cells, and five others consisting each of two cells which form an envelope round it. 
The lowermost cell of the axial row is the nodal cell, the second remains small and 
colourless, and corresponds to the first ' Wendungszelle ' in Nitella. It becomes in this 
case also, as De Bary's drawings show, separated by a somewhat oblique septum at 
the base of the apical cell (now the third of the axial row). Originally almost hemi- 
spherical, the apical cell grows first of all into the form of a narrow cylinder, and 
then becomes ovoid; it is provided, until it attains its full size, with a thin very 
delicate cell-wall. Drops of fat and starch grains accumulate in its protoplasm: its 
apex however remains free from these, and forms a transparent finely granular terminal 
papilla, the receptive portion. The protoplasm of the apical cell of the carpogonium 
has therefore become transformed into an oosphere. The five enveloping tubes are 
from the first in close contact with the apical cell ; after each has become divided by 
Fig. 202. Development of the carpogonium of Nitella flexihs (x about 300); 
X ' Wendungszellen.' 
a septum about half way up, the uppermost of the cells thus separated also become 
closely united with one another above the oosphere. This closing of the envelope 
takes place at least in Chara fcetida, before the ' Wendungszelle ' has separated from 
the oosphere. The five upper cells of the envelope are at first as long as the five 
lower ones, and the septa which separate them lie about half way up the oosphere. 
As it now increases in size, the five lower ones become elongated into long tubes, which 
are at first straight but afterwards wind spirally round the oosphere. The five upper 
cells form the crown, which is elevated some distance above the apex of the oosphere. 
Between the crown and the apex of the oosphere the enveloping tubes grow inwards 
and increase in breadth, so that together they form, above the apical papilla of the 
oosphere, a thick diaphragm open only in the middle, by which a narrow space lying 
below the crown is separated from a still narrower one above the oosphere. The cells 
of the crown form a closed cover above the upper space ; the upper and under space are 
united through the narrow opening in the diaphragm. De Bary found a similar struc- 
ture in Nitella. As soon as the carpogonium attains its full size, the small space above 
the diaphragm enlarges, while the tubes between the diaphragm and the crown grow 
longer. This part of the envelope, which only attains its full size at a late period, 
De Bary calls the Neck. The tubes now separate laterally from one another, forming 
five clefts below the crown and above the diaphragm. Through these clefts the 
